How much extra Ram do I need to obtain realistically 'liveable-with' performance (or should I just leave it in OS9?)

I wouldn't wish OS9 on anybody who had a choice. While I don't know what OSX requires, I can't imagine it needing more than 256MB of RAM.

Following on from this - is it me or has the price of RAM gone through the roof? I bought some for a Quicksilver last year from zytech but the prices for all RAM seem to be a lot higher than then ($400 for an imac, then $200 to put a 512k stick in?)

I use standard RAM in my Macs. I've had dealers try to charge me more than twice the normal price of the RAM, and I refuse to pay that. The G4/500s at work run happily with normal PC133 (which is compatable with PC100), available from places like Austin:

Hyundai 512mb PC133     $149.00

I think newer G4s take DDR but I don't know what speed grade (DDR266, DDR333 or DDR400) or which models need it. Installing RAM in a G4 is trivial - I don't know what's involved for an iMac.

I don't have any problems that can be traced back to memory issues - we do have problems, but they're related to QuarkXPress and the use of an NT4 file server.

Craig Ringer