Most likely it won't be SETI@Home or Folding@home or even Genome@home becasue those three are the most competitive and it would be way too late to enter in, and think to make any real headway. The most logical choice would be something like the smaller ones like Distributed Folding, United Devices, or Find A Drug.
BTW I'll didn't list my comps to be folding:
Tbird 1.48ghz
Tbird about 1.4ghz
750 or so celeron
Celeron 566
G4 400
Imac 333mhz I think
bunch of friends computers that will be BORGed
and hopefully my watercooled folding (or whatever we run) monster project with at least 5 cpu that are at least 1.2ghz