I'm not here anymore, as a Linux user I've sauntered of nonchalantly :)
I'm not quite sure what you mean, but if I've got it right then you have a G3, a PC, 2 monitors and 1 keyboard mouse?
If you installed OSX onto the PC then it could do away with the synergy but you'd end up as a dual boot system so you'd have to restart every time, which is probably more of a pain than synergy!
Have you considered a KVM? or as another option virtualising an OSX install on your PC (you will need a meaty PC with a Intel CPU and plenty of ram) but then you could run OSX in a window.
http://www.redmondpie...re-windows-7-9140301/