If you can get Vista booting, then follow these commands.
1. Open start menu and type cmd.exe in the searchbox. Dont press enter. When the file comes up in search results, Right Click on it and select "Run As Administrator".
2. Now run the following commands 1 by 1.
Code:
bcdedit /create {legacy} /d “Windows XP Professional”
bcdedit /set {legacy} device boot
bcdedit /set {legacy} path \ntldr
bcdedit /displayorder {legacy} /addlast
After this restart the system and you'll find XP and Vista Dual Boot option.
Post here if you have furthur queries.
I hope this will help you out.