Well since we last spoke, the G5 has had it's innards cleaned and is now cruzin quite happily running Leopard.
The cleaning didn't stop at just cleaning the PCB's and fans, I had to open up the PSU which was FULL of fluff and dustballs, and the superdrive was a non-runner - intermittent read faults and consistently failed on write tasks.
Upon reassembly I replaced the superdrive with a standard dvd-rw drive and installed OSX 10.5. What a dinger! Running great with 1.5 GB Ram, but that sounds a bit mean doesn't it? 1.5Gig, well now it has 5.5 Gig, and when I get round to it again I'll retire the original pair of 512's and replace with a matched pair of 1Gig sticks, then retire the the pair of 256's the same way. Best to do them in pairs, so I can see if the replacement RAM is compatible, one pair at a time. Must say I've had no problems with the RAM which was a kingston kit from Elara.ie - not specifically for a G5, but all the Specs matched, and they are CL3 (3-3-3)