Start up with the Vista CD and select recovery options. Boot manager will be repaired. Repeat this until you get started Vista. Now you must edit the boot file so we can restore the boot menu. The easiest way to do this is to install BSD from this site. This program is largely self-explanatory. Click on "add a new entry" and type the name of the OS and drive letter. Finally, save and exit. Restart your computer. Start-up menu will be in place again, and you have the opportunity to choose OS like before.