depends if the time machine is on the Ubuntu partition or not.

if you reinstall vista it will wipe the mbr and leave your ubuntu
install untouched but the machine booting directly to vista.

Reinstalling Vista is not an option. I need to find a way to change the MBR to
point to Vista instead of LILO.

You will have to change the mbr to remove the pointer to grub. I use a
Knoppix CD for this. The procedure is to boot into the CD, bring up the
terminal and type sudo install-mbr /dev/hda , this will replace the mbr
with a generic Windows version. You can then use the partitioning tools
to either format the Linux partition to Windows format or increase the
size of the Windows partition to fill the hard drive.

You could edit the grub menu to remove all entries other than the windows entry
and set the timer to 1 second.