You start it like any other project:
1 Go to Tools and select Attach to project.
2 Type in http://freehal.net/freehal_at_home/
3 Select New User and enter email/password
4 When it attaches click finish and you will get one wu (default).
5 Go to My Account at FreeHAL and select FreeHAL preferences and select 25 as max wu's.

EDIT: corrected email/password

It is very surprising to me that you can run 8 WCG work units and any other work units. I went up and tried it. Very interesting... Thanks for the education DM, Chris, Jonathan. I will watch the memory now. As a side light I can't put the value of FreeHAL contribution in the same ballpark as WCG projects (In my case Cancer projects) but it sure is an interesting configuration.

MyOnlineTeam Daily Statistics for 02/14 - Active Members

Active team members report
==========================

                                                     Current          Points
Active member name            Rank      Change       Points        This Period
=========================     =====     ======     ===========     ===========
marysduby                         1          0      43,030,591          46,325
RT                                2          0      32,184,852         105,956
Coingames                         3          0      22,009,975          51,851
parmesian                         4          0      20,016,547          24,395
nl59056                           5          0      15,035,142               0
Dave Bell                         6          0      12,074,060          14,384
Esteban69                         7          0      11,361,667           4,531
keithhenry                        8          0      10,440,272          16,383
Jonathan Figdor                   9          0       8,084,028               0
brown chris                      10          0       7,097,755          28,897
NiceMedTexMD                     11          0       6,972,616          42,180
Fanie                            12          0       6,778,978             315
xroule                           13          0       6,339,174               0
frans6nl                         14          0       5,981,110           4,480
sulcata                          15          0       5,487,364           5,056
PohSoon                          16          0       5,462,861               0
Vuj                              17          0       4,930,725          22,049
Blueprint                        18          0       4,484,744           8,456
Tomwp                            19          0       2,659,528           5,202
Alain Bryden                     20          0       2,586,415               0
lawrencehardin                   21          0       2,401,950           2,010
wrr                              22          0       2,052,768           2,094
siseberg                         23          0       1,826,604               0
Sunny L. Kae                     24          0       1,793,235           1,578
Wunderwuzzi                      25          0       1,728,942             497
smcclarigan                      26          0       1,712,106           4,194
largethunder                     27          0       1,651,178           2,403
johng                            28          0       1,484,200           4,324
darth_vader                      29          0       1,212,322           7,325
harry_i_c                        30          0       1,146,376               0
Airwolf_Liu                      31          0       1,039,931           2,535
Jockin                           32          0       1,012,013           4,920
laughing66607                    33          0         984,342           1,520
Bravehart                        34          0         871,922           8,773
elpe                             35          0         817,522           2,278
imin                             36          0         814,371           1,606
Rene Punt                        37          0         642,016           3,687
Bon Kuhlman                      38          0         592,851             639
Momentary Lapse of Reason        39          0         341,835             490
barney15c                        40          0         287,908             664
madambaster                      41          0         265,970           1,172
WindmillMan76043                 42          0         263,465               0
Natalino                         43          0         253,701             709
Daeloan                          44          0         226,995               0
Dean Mullins                     45          0         141,915               0
Mechanical                       46          0          47,215           1,965
hne12359                         47          0          18,941               0

Note: Active members are those who earned points in the prior 30 days.

Top Twenty active members returning points today:
01: RT - 105,956 points
02: Coingames - 51,851 points
03: marysduby - 46,325 points
04: NiceMedTexMD - 42,180 points
05: brown chris - 28,897 points
06: parmesian - 24,395 points
07: Vuj - 22,049 points
08: keithhenry - 16,383 points
09: Dave Bell - 14,384 points
10: Bravehart - 8,773 points
11: Blueprint - 8,456 points
12: darth_vader - 7,325 points
13: Tomwp - 5,202 points
14: sulcata - 5,056 points
15: Jockin - 4,920 points
16: Esteban69 - 4,531 points
17: frans6nl - 4,480 points
18: johng - 4,324 points
19: smcclarigan - 4,194 points
20: Rene Punt - 3,687 points

Total points returned today: 435,843
Active members returning points today: 36
Average points per member active today: 12,106.75

That's for sure!

Yes, this is proving rather interesting. I have 56 WUs crunching at a time now on my quad and C2D. Both have 2GB of memory which is pretty much the minimum you need these days. In about 1.25 days on crunching FreeHAL, I already have over 9K BOINC credits - that would be 56K points over at WCG. Each FreeHAL WU takes 1.5-2 hours to complete on my machines and is good for 15 credits each. Memory starts out very low and grows as the task progresses. When nearing completion, they are each using just over 9MB of memory. That's 225MB or so max. If all you do on a machine is crunch, and in particular just WCG, you should be able to run the full 25 concurrent FreeHAL WUs ok. Task Manager shows zero percent CPU so it would support the no impact thought. However, while I'm not an expert on virtualization, there would seem to be some amount of work involved in running and managing the virtual tasks. So far though, I can't see any big impact on my other crunching. I've been running just WCG and FreeHAL for the past 24 hours and just WCG for the 24 prior to that. My WCG points for today are slightly less that yesterday but I can see that difference just from when the WCG tasks hit during the day. I did return two fewer WCG results today that yesterday. Looking at it in terms of points per WCG WU, it's down 18-20 points today vs yesterday. I ran only HFCC WUs on both days. I would suspect more memory might help but I'm a case of someone running minimal memory on the old C2D and quad CPUs (about 2.25 GHZ) machines and I would say any impact of running FreeHAL is minimal. Now, if you're doing real work on a machine or crunching other projects that use lots of memory (like Lattice), you may not be able to run FreeHAL or at least the max of 25 concurrent WUs. Of course when I'm crunching Lattice, I only crunch one Lattice WU at a time anyway and that's without FreeHAL. It doesn't have the appeal as a project that WCG has but I've just increased my daily BOINC credits 4X-5X just by adding the one project without hurting my existing crunching. Who'd have thunk it!