Where are you at with this problem?
If it was my system, I'd ask one simple question...
Was it part of the intial XP setup...nope! Then un-install it.... But, how you ask?
If there are no other ways to un-install it the obvious way, then if it was may system I would...
[a] [Unfortunately, I do not know of a freebe to do this. I use "Registry First Aid" for all of my registry needs ...especially in this sort of situation. There are others.]
...[b]SAVE AN EXPORTED COPY OF HE REGISTRY TO YOUR BACK UP FOLDER... I use c:\REG-BACKUPS and I title each, like "Uninstalled Oracle" If everything goes belly up later, just return here to restore the registry.
1. open regedit
2. find the word "oracle" and delete every reference.
3. return to Explorer
4. go to the folder in which Oracle was installed
5. delete all of its contents
6. use Unlocker, as suggested previously
7. run sfc_/scannow to ensure a safe reboot later
Hold your breath, insert diskette 1 from the XP set of boot disks...just in case...
Reboot and see if anything changed.