The iMac G5 I was given is working - 2gb RAM, 1.8ghz, and now 500gb hard drive. Unfortunately the drive is currently held in by Meccano, not the correct cradle - which also incorporates a fairly important heat sensor - so I've ordered the cradle on eBay. I've also ordered an Airport Extreme card, so the total to get this up and running will be about £35. Apart from that it needs a lot of cleaning - there's grunge which looks like cigarette tar in the internal ventilation ducts, and what appears to be blobs of candle wax and general greasiness on the outside. It'll come off, but I don't expect it to be easy.
What I really need, for this and for my iBook, is the family (multiple installations) PPC-compatible version of OSX 10.5 - not essential, I've put on 10.4 and it works, but desirable since it supports later versions of Safari, flash, etc. that address some of the site compatibility issues I've encountered. If anyone in the UK sees it on sale cheap somewhere please let me know, eBay and Amazon prices are a bit too high to justify the expense. I've looked at using a PPC Linux instead, but I'm really not very impressed with the ones I've tried.
At the moment the plan is to keep the iBook G4 as my bedroom computer if I can sort out its issues; sell the iMac G4, which is a bit on the slow side, more of a collector's computer that a working machine; and probably give the iMac G5 to a niece or grand niece/nephew.
But this will probably be in the New Year, really don't want to mess around with courier companies etc. at this time of year, and to be honest I don't WANT to sell the iMac G4, it's so pretty.
Powerful rare earth magnets allow some interesting tricks - this one's a self-propelled "train" made of a battery and some magnets, running inside a copper coil. If I was working I'd probably want to try this, though I'm willing to bet it kills the batteries (which look like small camera batteries such as AAAA) fairly quickly.