Reinstallations of Windows can be a real bear. Personally, I think reformatting
and reinstalling everything is best. That way, you're assured that years of detritus
is removed from the Registry.
But it is possible to leave XP in place and rebuild it. For that, you'll need a Windows
installation disc. You'll also need your Windows product key. That should be on a
tag on your computer. Or, it might be on the installation disc packaging.
If you don't have the product key, use
Belarc Advisor
 to retrieve it.
Ready? Put the Windows installation disc in your CD or DVD drive. Then reboot. When
you see the message, "Press any key to boot from CD," press Enter.
If you don't see that message, you need to
change your boot order
.
The installation CD will take you through several setup screens. If you installed
Windows XP, you'll probably recognize them. You might also be concerned that you're
on the wrong road. You're not.
On the fourth screen, you'll see a repair option. Ignore it. Select "To set up Windows
XP now, press ENTER." On the seventh screen, you're given the option of repairing
Windows or continuing setup. Highlight your installation of Windows and press R.
Windows will start replacing damaged files. It will leave much of the Registry in
place. Once the files are selected, Windows will reboot. Before it does, remove the
installation disc from the CD or DVD drive.
When the computer comes back up, you'll be asked for your product key. Enter it.
You'll see the usual setup screens as Windows goes along. You're doing fine. Eventually,
Windows will reboot. When it comes back up, you'll be at the Welcome to Microsoft
Windows screen.
Windows finishes file installations and configurations, and reboots. You're done.
You won't have to spend the next three days installing software and hardware. You
also won't have to reconfigure your networking setup.
This process is much faster than reformatting and reinstalling Windows. However,
if you have Registry problems left over from old programs, they may still be there.
In that case, I'd reformat and reinstall everything.