Woa! This reminds me of a few sayings, like "don't toss the baby out with the bathwater" or, got a splinter in your finger?? Don't cut off your hand as a way to remove it.
There is a reason why your computer won't start up. It can usually be fixed from the keyboard. No need at this time to trash the XP install because of a little trouble,,, ok.
First, Restart the computer and peck (don't hold) the F8 key, once a second while it is starting.
Eventually you will get a B+W screen with many choices on it.
Try selecting to prevent windows from restarting on error. (similar words, may be slightly different).
Now it will not restart over and over again, but will crash with a blue screen that has some words and lots of numbers. We need the error description and the numbers that follow, like...
aford10 - I can't boot into anything. Any option I choose the unit just goes into a reboot when the Windows splash screen comes up.
accolite - It seems I did install a program I had downloaded from download.com to use for disc cloning.
Tigsounds - Please don't think I'm ungrateful, I appreciate the help and suggestions. However, I didn't include a model number because my original question was generic in nature, not model specific, having only to do with reformatting a partition. The computer is a Sony PCV-RS420.
Yes, it can be done for just 1 partition. There is often a choice for a non-destructive restore. This will basically just fix your system files, and may allow you to boot up again. If you have the option, try this first.