How to rename system drive letter

After installing XP in a system with a second (used)
drive, I found that XP Setup had named the first (system)
disk E after formatting it to NTFS. I now see the second
drive as C even though the computer boots to E. I let it
go at the time and have worked with the system long enough
to not want to rebuild and reinstall everything on it.

The problem is that many programs default to C and I
myself sometimes forget that the system drive is E. I
know this is going to give me major headaches in the
future if I don't manage to get the system volume named C.

Disk Management will not let me rename the system volume,
nor will anything else I can find. I think this may be
related to "static drive letters", but I am in over my
head with this as I have not dealt with NTFS before.

Any advice would be appreciated.