Well, I made a bootable DVD of Win7 (finally, it wasn't easy since I downloaded the .exe files...)
It did a startup repair but now just boots into XP (which I installed onto the old drive again in order to go on this forum and write the DVD)...
Just going to format this HD again and reinstall windows. Can't be arsed! At least this time I can get C:, D: etc all in order finally.
Edit: if anybody else wants to turn the Digital River download into a bootable disc, follow these instructions: