Install EasyBCD 2.0 beta
after doing quick forum registration there to use beta.
You'll also need to install Net Framework 2.0
to run Easy in XP.
Add Windows 7 on Easy's Add/Remove tab by Name, Type, and correct drive letter, Save, Restart.
If this fails, you'll need to restart Windows 7 to install Easy there to Add XP which works better. This is done by marking Windows 7 active in XP Disk Mgmt., then boot Windows 7 DVD Repair console or Repair CD, clicking through to Recovery Tools list to run Startup Repair up to 3 separate times with reboots until Windows 7 starts