Having failed to really get any of the above working - I couldn't seem to get anywhere with a boot up disc since DOS didn't recognise the NTFS drive - I decided to buy a new hard drive. Spent £60 on a 320GB Seagate drive and stuck Windows on that. When I made the old one a slave, Windows did a chkdsk and found errors and "fixed" them.
I can access data on the old drive (which is good) but nothing is ever easy... I did try to replace the "system" file with one from a system restore file and when I tried to boot up with the old drive I appeared to be getting somewhere with the XP splash screen but then a BSOD.
Anyway - new problem is my new hard drive. It seems painfully slow - complains that all drivers are unsigned, doesn't recognise my USB card - despite installing the Belkin drivers. I also had problems when installing Windows the first time on it but not the second. Won't let me do Windows updates either - just seems to get stuck.
Sigh. So Ive decided to call it quits - the new hard drive seems crap but at least I can get data back. Think I might buy a new PC - so fed up I might even get one from PC world just so I can have a proper PC again!
Cheers for all your help though!