Download and boot from a Linux Live CD (I would suggest Ubuntu). This will give you access to the filesystem, so you can archive off important files. If you don't have an external disk to save them to, you can create a folder off the root of C:.
If you don't save to an external drive, when you re-install Vista, you will have the option to re-format the disk - don't. Over-installing Windows will create a backup of the previous Windows installation, probably in a folder called Windows.old.
I'm uncertain how it handles user files. It might leave them intact, it might back them up in Windows.Old, or it might wipe them. Therefore your backup (in the folder you created via the Linux Live CD) will save the day. This folder and all your other, non-system folders (program files etc) will be left intact.
Obviously, if you do have an external disk, you can simply wipe the machine entirely, and start again.
PS. In case it wasn't already apparent, I wouldn't bother trying to uninstall all drivers - you are best off with a clean sheet...