I'd say, only fold on the server if electrisity isn't an issue. You might get 2k PPD of the CPU but I'd guess at less. My dads old computer had an A64 X2 @ 2.25ghz and put out 1k PPD.
If you can get the GFX card folding on Linux that might be good for around 2k also. For a short while I ran a 8600 along side a 8800 but stopped because my voltages dropped a bit more than I was happy with (was only using a 480w (20a 12v) Tagan PSU). IIRC I got around 1.5k PPD but it was a passivly cooled card so the clocks may have been lower.