Boot free Partition Wizard
bootable CD, rightclick on Windows 7 partition to Modify>Convert to Primary, click OK.
next rightclick on Windows 7 partition again to Modify>Set to Active, click OK.
then click on Windows 7 HD to highlight it, from Disk tab select Rebuild MBR, OK, Apply all steps.
If Windows 7 doesn't start at reboot, boot into Windows 7 DVD Repair console or System Repair Disk
to Startup Repair - Run 3 Separate Times
Once Windows 7 starts on its own, confirm in Disk Mgmt it holds the System Active flags.
If you want to recover the XP HD space into Windows 7, boot PW CD again to rightclick XP to Delete, OK. Then rightclick Windows 7 partition to Resize, slide left grey border to the left to take up XP space, OK, Apply all steps. You may need to Rebuild MBR again or run Startup Repairs if Windows 7 doesn't start.
Back up your files and a Windows 7 backup image beforehand.