drive letter problem

I recently put a new hard drive in my computer. When I
finally got all the data off the old drive that is just
before crashing, it came down with a bad case of SIDS--
system ID syndrome. Sysprep wouldn't work, so I ended up
installing XP on the new drive. It finally booted by
itself, but the computer calls it G: instead of C:. I
tried using disk management to change the drive letter,
but it won't let me change the letter of the boot disk,
etc. I am still having to use a flakey drive for C:

What can I do, short of formatting and starting over?