NTLDR is missing

Issue: Error :NTLDR is missing after Windows Vista installed and Xp wont boot up.

After some digging around the internet, I found the solution:
Boot up Windows Vista, and navigate to Start (the Vista orb)-> All Programs -> Accessories -> Command Prompt, then right-click on Command Prompt and select Run as Adminstrator. Either enter your password if needed or just press continue. The new window should be titled "Administrator: Command Prompt". In the command prompt, type in bcdedit /enum active and press Enter. Locate the sections titled "Windows Legacy OS Loader". Note the identifier (all of them if there is more than one matching section); my identifier was {ntldr}. If the problem is the same as mine, the device property should be currently set to unknown. Use the command bcdedit /set (ID) device boot to change unknown to boot, that is, the partition that is active and is booting from. By default, Vista does not change which partition boots, so if your XP partition is set as active, it will add the new booting code to that. Therefore assuming your XP partition is set as the active (boot) partition, the above command will be correct. Apply the above command for each identifier, replacing (ID) with the identifier itself, including the curly braces, e.g. bcdedit /set {ntldr} device boot. Press Enter after each one - it should report that the operation was completed successfully. Rerun the command in step 2 to check that the changes were applied correctly. Test!
Note: Can refer this link to understand BCD EDIT command
http://technet2.microsoft.com/WindowsVista/en/library/85cd5efe-c349-427c-b035-c2719d4af7781033.mspx?mfr=true