Hi! Preston,
the first thing you should try is to load the last know configuration. After your computer boots up.. Hit "F8" key until you see the screen which lists all the boot options.
Select "Last known Good Configuration"
If this doesn't work, try this solution from Microsoft: http://support.microsoft.com/kb/307545/en-us
Since the last method of the two requires expertise.. and if you don't care too much if you lose one or two of your programs, then you can try an easier way of "In Place Upgrade"
here are the steps:
http://support.microsoft.com/kb/315341
This can be done by any cd as long as it is the same OS (XP Pro/Home etc.) and you should have your Product Key ready as well.