Long story short, I used Powerquest Partition Magic 8.0 to forcibly change my C: partition (which had Windows XP installed on it) on my IDE HDD to something else (like D: or something) and changed a different partition on my SATA HDD (with Windows 7 installed on it) to the C: drive. I did this so I could boot from the SATA HDD, but I still can't do this so the problem hasn't been solved. But to make matters worse, now I can't even boot the Windows XP because it isn't the C: anymore! I just get the Windows XP startup screen but not my username or password prompt.
Since this hasn't solved my initial problem, and I would still like to have XP working, what can I do to solve this?
I did not create a Partition Magic boot floppy or CD.
Dang, you were supposed to take PM8's suggestion to let it re-map the drives when you did that. You cannot access PM8 because you cannot get to WinXP. If you have your WinXP CD, you may be able to do a repair install of XP, Mr. Stevens has a step by step guide here. I've done it several times (learned a lot from experience, I guess).