Windows XP forum: Need help changing boot drive letter

Hi guys and girls,

I am supposed to fix up this old desktop pc for my grandmother, and trust me you don't wanna know how old it is. The problem I was trying to fix was that the OS was installed on a small 40 gig hdd from ancient times, that was barely able to move with XP. Since the PC had like 70% free space on a second hdd that was an 80gig Seagate with 7200rpm, I wanted to shift the OS from the first drive to the second.
Since I have an in with a buddy from a tech support service he gave me a bunch of boot cds. So I moved the two existing partitions on the second drive to the end of the drive, and copied the original system partition to the second drive's beginning. Then I popped the pc open and switched the IDE cable (yeah, I know) so that the second drive was at the master position and the first was at the slave position. New system partition was made active, and the PC did a boot from it just fine. Problem is that none of the software would run properly since they were all installed to the C: drive and the new partition was D:.

So I monkeyed around with the boot CDs (didn't use partition magic because it showed an error 106) and using easeus i rebuilt the mbr on the new drive and removed the ancient one.

When I tried to boot again, it got to the welcome screen and just sat there. Now if I insert the original drive, set the xp partition as active and rebuild mbr, it boots just fine, but the problem is that it boots from the old c: drive.

So, can somebody please help me out and tell me a program that can, without booting windows change the system drive letter.