System won't restart after 11/25/2007 updates

On 11/25/2007 I logged onto the Microsoft website and downloaded updates onto
my system. I selected updates due to the problem that when I start Word my
system tried to install from disk missing files. This is a preinstalled
program so I have no disk. If I cancel the install the program opens and
seams to work fine anyway. So I used Microsoft update to hopefully fix this
problem. On rebootiing, my system starts Windows XP, gets to the desktop and
then shuts down to begin again. Since I can't run windows from that hard
drive, I have installed, temporarily, to an other hard drive a borrowed
version of Windows Vista. How do I 'go back' manually? I can access the
drive and all files on the drive. Is there a diagnostic I can run on hard
drive E to check hard drive F?