In XP you can indeed disable the default Administrator account, and indeed all Admin-level accounts. This, however, leaves you unable to do anything which requires Admin rights like install software, get updates from Microsoft, and a score of other things which you want to be able to keep doing. In order to do these otherwise mundane tasks you would have to reboot the computer into safe mode, re-enable the Admin account, reboot back into normal mode to do whatever it was you were doing, then re-disable the admin account.
A better strategy is to only use the Admin account when necessary and to have a good, strong passphrase for it (a passphrase
is generally longer and more complex, hence better, than a password and is usually easier to remember)