In Folding@Home we could really use some help right now, as we happen to be dropping in rank like crazy (we're down to 21 already and going to be 23 before too long).
Folding@Home works best on broadband, but it also works fine if you have a demand-dial connection (like me). Unfortunately, anything under about 300MHz won't be able to meet WU deadlines, so you might want to find something else (like DPAD) for those systems. The graphical client is fine if you stay logged in all the time, but you can also use the command-line-interface client if you want to set F@H up as a system service in Windows NT, 2000, or XP (then it would run even with noone logged in). I highly recommend that you do not run the screensaver, as it has "issues" and isn't very efficient either.
When setting up the client, you can (and should) use the same username for all systems. Just enter 198 for the team number (that's the number of Team AnandTech).