This happens quite often and its messy. Both OS are most likely on the same partition and you will have no end of software problems, conflicts, and confusion. Its bad enough when they are on separate partitions. If you go and find xp home and delete it piece by piece you end up with a non - booting system because xp pro is booting from xp home.
You can do this but you will need to copy boot files to xp pro and run the fixboot command. A repair install of Xp pro would be easier as long as you don't end up with two again.
If it were me, I would boot from the xp pro cd and start fresh. Delete all partitions, re-create partitions and format them. Make a 10 gig partition for xp and leave the rest for data. This is safest. Then reinstall xp pro.
It will take a little study and a little reading. Here is a good place to start.
http://www.blackviper.com/Articles/O...tallxppro1.htm
http://www.webtree.ca/windowsxp/repair_xp.htm