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#21
As stated, the only reason to convert Win7 from Logical to Primary is so it can be marked Active so that the MBR can be recovered into it to start it up. Then you can install EasyBCD which works better from Win7 to add XP.
If you did in fact convert Win7 to Primary, to boot it now you will mark it Active from XP Disk Management or Partition Wizard, then boot Win7 DVD Repair console or Repair CD, click through to Recovery tools list to run Startup Repair up to 3 separate times with reboots to write the MBR to Win7 and start it up.
Next install EasyBCD 2.0 beta to add XP from Win7, accept offered boot files, allow to autocomplete, Save, Restart.