QUOTE (Ed_P @ Apr 27 2011, 01:35 AM)

I have the primary hdd's MBR backed up, in addition to all it's partitions. Could I backup the current MBR, restore it the the 2nd hdd, then restore the backed up MBR of the primary hdd to the primary hdd? Would that work?
NO.
The MBR (and the bootsector also) is made of TWO parts:
- DATA
- CODE
CODE is generic (and specific to the actual OS the MBR came from).
DATA is specific to the disk and contains:
- partition table
- disk signature
You CANNOT backup a MBR and restore it to another drive (unless you want to "clone" it.
Right now your first hard disk MBR contains:
- first hard disk DATA (partition table and disk signature)
- Windows 7 CODE
Right now the bootsector in the Active partition on your first hard disk contains:
- Active partition on first hard disk DATA (volume label and geometry)
- Windows 7 CODE
Before your first hard disk MBR contained:
- first hard disk DATA (partition table and disk signature)
- Windows XP CODE
Before the bootsector in the Active partition on your first hard disk contained:
- Active partition on first hard disk DATA (volume label and geometry)
- Windows xp CODE
If you have a backup of the whole MBR and of the whole bootsector you can restore them to the first hard disk and be in the same booting situation as before, without needing to use MBRFIX and bootsect. (which would replace the CODE leaving the DATA UNTOUCHED).
The hardcoded path are obviously in the Registry but thinking to manually editing them with Regedit is pretty much a NON-SMART idea.

(you are very welcome to attempt it and consequently botch an otherwise perfectly good 7 install though

)
You DO NOT *need* NOR *want* to install 7 on the SAME drive (in the sense of partition/volume, NOT "disk") you installed XP, as you will create more problems that you can count. Another drive/partition in the same disk is OK, BUT NOT the same drive.
Why don't you do like all people should do?
Plan BEFORE doing things, evaluate pro's and con's and only THEN do things?

The easy thing to do is (in your setup) has been already told you.
This would leave XP "as it was before" and allow you to boot through grub4dos the Windows 7 install on the second drive (with the letter Z: you assigned it), if you remove the first drive and use it as "first drive" you will be able to boot directly in Windows 7 (still with letter Z: assigned to it).
If this is not your wanted result, express your wishes, and I will try suggesting you the easiest path to get it (if possible).
While you think about this, do READ this (simply read "7" instead of "Vista"

):
http://www.multibooters.co.uk/(AT LEAST these pages):
http://www.multibooters.co.uk/mbr.htmlhttp://www.multibooters.co.uk/articles/drive_letters.htmlhttp://www.multibooters.co.uk/multiboot.htmlhttp://www.multibooters.co.uk/system.htmljaclaz