Use GRUB...which should have been an option when installing Ubuntu.
Reinstall Ubuntu using the install disk, and click advanced on the last screen before allowing it to go to town...allow it to install GRUB on the primary hard disk.
If, at some point you decide to get rid of Ubuntu, you will need to run FIXBOOT and FIXMBR. I believe that, in Vista, to use FIXBOOT and FIXMBR there is a special command you have to use in the recovery console other than FIXBOOT and FIXMBR.
GRUB does not support booting into Windows alone, for some odd reason, although i believe that support should be added.
