[MTUSUPPORT]

Try this, Last ditch, but you said your under Xp right?

Try Right clicking on the mstudio421setup.exe file, then left click on Properties.

Click on Compatibility Tab, and turn it on. Try setting it to Windows Xp, if thats an option. I just did this on a customers computer, but theres was Windows 7, 64 bit, and it would not install with the same error your getting.

No clue why, as it should work fine. Let me know what you find.