Howard,
If you just installed the WindowsXP with out any other user installable
programs than what Lance pointed you to may be sufficient. BUT, if you now
have some other programs installed then it could get ugly and even to the
point that it probably be better to just re-install the OS properly. The
reason is that some programs do not follow certain guidelines and may have
drive letter pointers coded in such a way that simply changing path pointers
and registry entries may not work.
What I mean by installing OS properly is that your system drive is C. The
drive letter C is the best choice only because of that unknown program that
you may have or get later that only understand C as the default.
To insure that the letter C is chosen by the WindowsXP install, you need
to remove any hardware that may fool the installation in to thinking that
there is already drive C and that drive C is not suitable for installation.
One such device that comes to mind is a IDE ZIP drive that the installer
will see as such. You need to actually unplug it during the installation.
USB drives will also create such situation and should be unplugged.