First in EasyBCD 2.0 try removing the XP listing on Edit Boot menu tab. Now try adding it back on Add OS tab, see if it offers boot files, accept them, let it autocomplete, Save, Restart to Dual Boot menu if lucky.
If not, power down to unplug Windows 7 HD, set XP as first HD to boot in BIOS setup then run a Repair Install on XP: Repair Windows XP - How To Perform a Repair Installation of Windows XP - Part 1 of 2
After XP starts up, power down to plug back in Windows 7 HD, set preferred HD as first to boot in BIOS setup, then boot the other OS HD using one-time BIOS Boot menu key.
If you prefer a Windows-managed Dual boot (which interlocks the HD's and makes them harder to extricate) then try removing XP in EasyBCD 2.0, add it again as given above.