Meanwhile....
Go Start>Run ("Start Search" in Vista/7), type in:
sfc /scannow
Click OK (hold CTRL, and SHIFT, hit Enter in Vista/7).
Have Windows CD/DVD handy (with Vista/7, most likely, you won't need it).
If System File Checker (sfc) will find any errors, it may ask you for the CD/DVD (rarely in Vista/7 case).
I realize you don't have that CD yet, but I just want you to check if "sfc" WILL ask you for a CD.
That way we'll know if some system files are NOT OK.