The smartest method to dual boot on separate HD's is to set Windows 7 HD first to boot, then when you want to boot XP use the one-time BIOS Boot Menu key at boot to trigger it's HD to boot.
To do this, unplug the Windows 7 HD, boot into System Recovery Options
on Windows 7 DVD or Repair CD to open a Command Prompt, mark XP partition Active: Partition - Mark as Active (Method Two)
Next in Diskpart type List Volume, get XP drive letter, type Exit to exit diskpart, then type: bootsect /nt52 F:
or whatever the XP drive letter is in WinRe.
Reboot, tap the BIOS one-time Boot Menu key given on your first boot screen to choose XP HD to boot.
If this fails, you can delete XP in EasyBCd then add it again, accept it's boot files, Save, Reboot.