Finally got round to putting a new hard drive in - delayed by 'flu. Much easier than taking the iMac to bits - took less than an hour to put together again. Started perfectly! I have installed LinuxMint rather than apple software - again went very smoothly.
(This was my wife's iMac. It was over six years old when it died, so rather than have it 'officially' repaired she bought herself a new one: bigger screen, bigger hard disc, four times the memory, Lion software etc. I got the broken one to play with. I also have her old mobile phone and her old her old iPod nano. Well, I am old, 70 in just over 3 hours.)
Apple certainly does not make it easy to repair their stuff, but it is possible with patience, a lot of bad language, and an occasional extra hand.
Andrew