well, the IRQ less than errors did go after I wiped the pagefile and got Windows to rebuild it. Now my issues are definitely hard drive related. I can't even install XP on another drive if my old main ddrive is still connected - instant blue screen.
Couldn't even use Knoppix with Captive-ntfs to try and sort the filesystem out - it just hung, so something major is up.

So anyway - currently building another PC, and I'll see whether I can get the old drive mounted in any way to grab the info off it. Not too much new since last backup, but enough for it to be a pain in the butt.