How to get back to the original system?

Today the mood to the next a preview version of Windows 7 installation, I had the XP system is not deleted, on the C disk, the installation of the system 7 is the other disk, and so on, but after I installed a good start menu, there will be no XP, there is only one system of 7, I do not know how can we get back XP system?

Edit boot.ini

[boot loader]
timeout = 5
default = multi (0) disk (0) rdisk (0) partition (1) \ WINDOWS
[operating systems]
multi (0) disk (0) rdisk (0) partition (1) \ WINDOWS = “Microsoft Windows XP Professional” / noexecute = optin / fastdetect
C:\ GHLDR = push-to-GHOST v11.0 Build 070315