What are the best projects to use with slower processors so they complete on time?

I would consider Help Conquer Cancer at World Community Grid and SIMAP when it has work.

I have WCG, Engima, Rosetta, SIMAP and Einstein running on a PowerPC G4/733. You may not get work from all of the projects all of the time, since some batches of work have higher memory requirements than others. I would just try a couple of projects until you find one that seems to have a good duration of WU for you; another consideration will be whether the machine in question will be on 24/7 or not. The BOINC manager is supposed to adjust itself so that it won't get more work than it can do before the deadline, though it may take a while before it balances out.

I binned the projects somewhat, and concluded the following (preferred applications):

• Non-CPU intensive:
  
http://freehal.net/freehal_at_home
http://surveill.dei.uc.pt/surveill
http://wuprop.boinc-af.org


• < 30min:
  
http://home.edges-grid.eu/home (EMMIL, PR, X-Ray, VisIVO, Laserac)
http://ibercivis.es/ibercivis (calibracion, criticalidad, cuanticables, iter, magma_test, materiales16, materiales24, materiales32, materiales48, nanoluz, nanotest, neurosim, pezevenchi, protomol, sanidad)
http://mersenneathome.net (TDT)


• < 1h:
  
http://casathome.ihep.ac.cn
http://www.distributeddatamining.org/user
http://escatter11.fullerton.edu/nfs (lasieved)
http://boinc.med.usherbrooke.ca/nrg
http://www.primegrid.com (Sophie-Germain)
http://boinc.bakerlab.org/rosetta
http://szdg.lpds.sztaki.hu/szdg (KOPI)

HTH

FreeHAL has endlessly problems. Either you get download-errors (caused by checksum or signature errors) or the project is offline/down and very much often you will get messages like "Not sending work - in a metaphorical sense, you are stuck in a traffic jam".
Surveill has disabled the account-creation...