Note : Before trying the step below please run startup repair first

Solution :

1. Boot the computer from Vista OS DVD.

• Click on Repair Your Computer.

• Click on Command prompt.

• At the X:\Sources prompt, type bcdedit /export C:\BCD_Backup and press <Enter>

• Type c: and press <Enter>.

• At the C:\ prompt, type cd boot and press <Enter>.

• At the C:\Boot prompt, type attrib bcd -s -h -r and press <Enter>.

• At the C:\Boot prompt, type ren c:\boot\bcd bcd.old and press <Enter>.

• At the C:\Boot prompt, type bootrec /rebuildbcd and press <Enter>.

• The Boot Configuration File will be rebuilt at this point. Once it finishes, type exit and press <Enter>. Click the Restart button

Here are some other commands

bootrec /RebuildBcd - Use this option when you must completely rebuild the BCD
bootrec /FixMbr - writes a Windows Vista-compatible MBR to the system partition
bootrec /FixBoot - writes a new boot sector to the system partition by using a boot sector that is compatible with Windows Vista

If the automated startup repair doesn't do it - even after a few goes , as Prasath says,

I would try this first

1. bootrec /fixmbr

2. your dvdrom drive letter:\boot\bootsect.exe /nt60 all /force

3. del C:\boot\bcd

4. bootrec /rebuildbcd

5. Close cmd prompt

6. remove dvd, Reboot.

Fingers crossed.