windows xp not booting after windows7 installation

There is a simple solution to get back the Windows XP. The problem often occurs after you install Windows 7 or Windows Vista as the second operating system (while XP was already on the computer).
You can get the boot loader to recognize Windows XP using the following four commands. To use these commands, invoke the command prompt by typing cmd in the Run menu.

type each of the following commands followed by the Enter key:

Bcdedit /create {ntldr} /d "Windows XP"
Bcdedit /set {ntldr} device partition=c: (assuming your xp was in drive c:)
Bcdedit /set {ntldr} path \ntldr
Bcdedit /displayorder {ntldr} /addlast
exit

software to do this automatically :

http://www.duckload.com/download/2061807/xp.bat

The last command will close the command prompt window. Reboot and you can see that the boot loader shows both Windows XP and Windows 7 (Or Windows Vista as per the case).
START---->ALL PROGRAMMES----->ACCESSORIES---->COMMAND PROMPT

Final note: BCDEDIT works from installation boot dvd too. If you mess up with a setting and you cannot boot, just boot from DVD and enter Repair Computer, then go to command prompt and there you go. You can play again with bcdedit to restore your system back