Key point, memtest does not catch all errors. Make sure you run at default speed, and that you have some o/c'ing headroom. I generally will relax timings, drop speed to default (200FSB), and keep the same memory voltage for install.
Are you sure you're using the correct driver disk? I mean, the one you select with F6 when you install Windows. Also, in BIOS you need to make sure your RAID device is set as the boot device (after the optical drive you're installing Windows from).
You might also look into a fix for the scratch on the install CD. Lots of people report success with turtle wax, but you might invest in a scratch repair kit. I've heard may success stories both with audio and data disks, never heard of someone applying the fix to a Windows disk, so if you go that route proceed carefully.