Have you tried getting into safe mode? press F8(I suggest you start pressing it like 50 times in 5 seconds) before the vista loading screen comes on. You should get some sort of boot menu, and the option to boot into safe mode.

I can't guarantee that it will work though.

If you are really desperate, boot a Linux live CD, and mount your hdd in Linux, and see what you get there. (I recommend searching some tuts first for this.)