Do it in the reverse order:
Once you get back into Windows XP setup and run EasyBCD.
Install the Vista Boot Loader from EasyBCD within Windows XP
Add the Windows XP boot option to the Vista Boot Loader through EasyBCD.
You should at this point be able to boot into XP.
The reason this would happen is because Windows XP drive letter reverts to the C Drive when you are booting it up however the Vista Boot Loader is telling the system to look on the E drive. It is quite confusing just know that if you run EasyBCD from within Windows XP the drive mapping will match up and all should work
Cheers!
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