Can you try to partition part of your F: drive and label it as C:? If you know how to do that, it should solve your problem. I'm not using an XP machine right now because I'm at work. I'll look at my XP machine when I get home, and I'll post instructions if I can figure it out. I've never tried to do that with XP, so I'm not sure of the details.
Edit: I did a quick google, and this is what I came up with from the Microsoft web site.
http://support.microsoft.com/kb/309000)
There's a section about 1/4 of the way down the page titled "How to create a new partition or a new logical drive", which tells you exactly how to add a partition or logical drive. And if it doesn't work, there's another section below that which tells you how to delete them. Good luck.