Shubham96,
Windows 7 replaces the boot.ini file for Windows XP -- which is why you are not able to boot from it. You will a. need 3rd party software to replace Windows XP back into the boot loader, or b.reformat and reinstall XP. For addtional assistance, and to learn more about Win 7, Microsoft does have an official Windows 7 RC Support Forum located here Link Removed . It is supported by product specialists as well as engineers and support teams.
Jessica
Microsoft Windows Client Team