i picked up a right bargain yesterday sunday 14th july a powermac g5 dual 2.3 from a music studio for £40 with dual hdd's 2 gb ram but it had the nvida 5200 gpu so popped the one out of my g4 and it ran morphOS very smoothly indeed, i installed MOS on the second hdd ready for when i get the mos key for it.
i will look at investing in a higher gpu like an x800xt or an x850xt or even the x1950xt for it.
make it a little power house

Great buy. If you're going to put an X800/X850 look rather for a Mac version (or flash a PC one, but that's a lottery and won't always work as expected). If you're going for a X1950 then make sure it's not too wide. I once got a X1950 that was 12 cm wide and that's apparently too much to fit it together with the plastic side deflector. Of course you could operate without it too. Moreover - the X1950 has no Mac version, so you're limited to PC version of the card. You'll need some power adapters to draw voltage either from SATA or Molex connector and of course Open Firmware or OSX won't display anything on it. MorphOS however can handle it. Good luck.