I'm an Intel guy, but I believe the 4400 would be hard put to make the SMP deadlines. They're so short - 3 or 4 days typically. Very disappointing to have done all that folding, only to see the deadline go by, and you're still folding at only 95%!
So I'd recommend two FAH uni-processor clients, either 5.02 or 5.04, one installed as a service, with big packets=yes, and the other installed as a console window, with big packets also = yes.
You've got the memory saxile!
The console window is just easier to stop when you need to do something that requires more computer resources, AND it's easier for a new folder to get to know the FAH client, if it's there as a window, also.
It's up 24/7 and idle 90% of the time?
I'd try the SMP client, then. If it doesn't work, you can always go back to the uni-processor folding programs.