At this point, we can best advise you if you post a screenshot of your full Disk Management map.
Use the Snipping Tool in the Start Menu, attaching file using paper clip icon in reply box.
The normal procedure is to mark the WIndows 7 partition active, delete the XP partition holding the MBR, then boot into the Win 7 DVD and run Startup Repair 3 times to rewrite the MBR to Windows 7.
This can also be done using EasyBCD beta Attachment 40032
which can rebuild the Windows 7 MBR.
Whichever you choose, back up your files. And let us see a screenshot to be sure we are advising you correctly.