Home or Pro?

In either case there is a built-in Administrator account. As mentioned this account is only accessible in Safe Mode in XP Home and in Pro you need to Ctrl+Alt+delete to access it.

When XP is installed you are asked to create a User account and this becomes the Administrator account that is generally logged into. Hence you have two Administrator accounts.

Anyway via either one you should be able to Create and/or Delete other accounts as long as there are two functioning Administrator accounts.

If you don't want to reinstall create a new Administrator account and delete the old one that was previously created. You cannot delete the built-in Administrator account but under normal circumstances no one ever knows this account exists to begin with.