A. The Vista media has a great recovery environment that you can use in this situation in two ways. The first (and most likely to succeed) is to boot from the Vista media and select the Repair My Computer option, which (after you select the Windows installation) offers a number of repair options. The first option is Startup Repair, which performs a scan of the environment and fixes problems that are preventing your computer from booting, including replacing the boot sector.
If this fix doesn't work, boot from the Vista media again and select the Command Prompt option. From the Windows PE command prompt, you can use the Bootrec command-line tool, which offers options to replace the Master Boot Record (MBR) with a Vista-compatible version, replace the boot sector, and rebuild the Boot Configuration Data (BCD).
To replace the MBR (which doesn't erase the partition table, so you won't lose your partitions), run the Bootrec /fixmbr command. To replace the boot sector use the Bootrec /fixboot command. Both commands shouldn't harm a healthy installation, so they're safe to run. After you execute the commands, reboot the installation.