Hi,
Since both drives already have an installed version of Windows the only thing to do is fix the boot sector of the first drive to be able to access either installation.
Boot off the WinXP cd and run the
Recovery Console. Then at the command prompt, type 'bootcfg /scan' <ENTER> (no quotes). This will scan all drives for Windows installations and allow you to add to the Boot Menu. If this doesn't work, try running FIXBOOT before.