Need help taking Windows off of my computer

Ok, so last week my computer has a melt down. I need to take Windows off my computer so I can reload it into the computer. Why can't I figure this out?

I reloaded XP into my computer thinking it would just override the previous Windows program but it has not done that. XP is up and running but when the computer starts up, it asks if it was Windows XP home version or Windows XP professional.

So that tells me I still have the old Windows.

Can anyone tell me how to delete this so I only have one windows program running? I'm using way too much disk space having both. Thanks in advance to whoever can help me.

Hey Jen. Email me... I can help you with it. :)