|You DO NOT need to un-hide the built in Administrator account !|
There can only be one user that is spelled exactly Administrator. By default, that's the built in Administrator user that, by default, you can only access on the logon screen when you load Windows into Safe mode.
There is usually NO NEED to change things so you're getting the Administrator user to choose when you load Windows normally.
You often see a message that you must be logged on to a user that is an administrator account or a Computer administrator before you install drivers or programs, but what they're talking about is not necessarily the built in Administrator user.
All users of XP have administrator rights by default - when you look in Control Panel under User Accounts it says Computer administrator for your user - that's all you need to have when you're installing software.
In other words, by default, you already have the rights to install software.
A user that has administrator rights - is designated a Computer administrator - can enable the built in Guest user, which always has Limited rights,
or - a user that has administrator rights can assign Limited rights to any other user (except Guest).
You can always install software if your user doesn't have Limited rights.