|Test the memory with Memtest86.|
Test the hard drive with utility from the hard disk manufacturer.
Set in the BIOS the boot order so the DVD drive is first in the boot order.
Windows 7 Basic, if you have at least 2GB RAM should be faster than Vista, especially on a clean install. Which ever you install, choose custom and delete existing partitions and create a new one to do the install on and format that. This will ensure that you are free of any infection and free of any leftovers from the slow installation.
You have to be a little bit crazy to keep you from going insane.