How to Remove Vista from a Dual Boot system
1. Boot your computer in to Windows XP.
2. Ensure you have the Vista DVD image emulated or in the DVD drive.
3. Go to Start and Run. Type in e:\boot\bootsect.exe /nt52 ALL /force (without quotes, and replacing e: with the drive letter of your Vista DVD).
4. Restart the computer, and you will notice the boot selection menu is gone.
Format the partition/drive where you had Vista installed.
5. Remove two files (Boot.BAK & Bootsect.BAK) on your XP drives root folder (C :), these were backup files of your previous boot loader, now no longer useful.
6. Optional: Restart to ensure it still works.
7. Use your partition software to merge your partitions together.
Now the complete system is out from vista and without the New Boot loader.
Thanks
E.Ravi