Start with http://support.microsoft.com/?kbid=315403
I just built a brand new system. Using a 3000+AMD CPU,512DDR Ram,DVD+RW Burner,Gigabyte GA-7VT600 Motherboard, MSI-FX5600 Video Card, 120gig WD HDD.
I am trying to install Windows XP Prof. It starts loading Windows then reboots, the Windows XP screen comes up.....and then the blue screen
with the Unmountable Boot Error code.
I have tried another new harddrive, Windows XP disk, Removed the dvd burner and installed a known good CDRW.
Still get error... anybody run across this before? I am very fustrated.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic