Can't change drive letter


My coumputer had Windows Vista installed on c:\
I also had another partition on the same drive called d:\
Into that partition I've installed Windows XP, and after that I've "repaired" the boot loader using Windows Vista installation disk, thus making Vista my default OS again.

Installed EasyBCD on vista, and now I'm trying to add the XP entry (which is at D:\), the problem is that the program doesn't let me change the drive letter in the "add entry" section (its stuck on c:\ written in grey (not black) meaning it can't be changed).

Any suggestions?

Thanks a lot..