I tried bootdisk.com , but it seems that most of the programs there are meant to run under Windows. I couldn't get Linux to create a boot disk using those programs.

Ah well. I did manage to fix it. I reinstalled Windows, but I installed it into a directory with a different name. Then, very surprisingly, Windows did what I actually would've hoped it'd do. It added the new Windows to the boot menu and kept the old one. Plus it renamed all my old folders for my documents and settings and whatnot to some sort of backup name so it actually kept them all. Windows boots fine now.

Not sure what the problem was. According to what I read somewhere, the agp440.sys file probably wasn't even the problem. Windows doesn't show all the drivers it loads as it loads them, it only shows some. agp440.sys was the last in the list, but probably not what was destroying my computer. In any case I've gone and disabled the stupid auto-restart option. Everything seems to work OK now. I'm going to let stupid Windows decide what graphics driver it likes from its own Windows Update collection and keep that one. Maybe that'll spare me.