Yes if you do an upgrade with Windows XP professional!I would like to know that if you install Windows xp professionnal on top of windows xp home edition if this would work???
But like George's points out, don't do it!your BEST move is a clean start... ...trust me, you have a high percentage to regret using the same partition..
I agree with George's suggestions, just backup your data. Clean your hard-disk and re-install from scratch! In my Oppinion you should create two partitions one for your data and the other for windows and programs you use!
Some people will tell you that these days extra partitions are not necessary, they are wrong in my oppinion; I have seen to many people loose they data because they have everything in one single partition and by some stupid reason windows reinitialized and cleaned up everything!
Finnally, if you treasure your data backup it frequently! cd/dvd's are cheap these days and they can save your data! You can even use an extra hard-disk(external one for example) to keep you backed-up data!...a backup is a good precaution...