I agree with Jorgie for the large part. I want to bring up another threat to companies' security I think they may not be aware of. If you set all your root local administrator passwords to be the same, and log onto one of those computers using that password, you can now access any of the other PCs or Servers on the network (with the same root account name and password, although a different machine name) as administrator.
Additionally, it's not possible to delete built in accounts, so the best you can do is rename it. Indeed, it is a best practice to then create an administrator account with a complicated password and no rights. So then, you must create unique passwords (or admin account names) for each built in local Administrator account for each PC on your network. You can then create a method to track all these passwords, should you need one. An alternative is to teach your IS Department how to reset them and let the IS Department run around arbitrarily renaming admin passwords as they work. This might not ensure unique passwords, and again, if the admin account name and passwords are the same on two computers and you log into one of them with the admin account you can then access the other as admin.
By the way, this goes for Server Class as well (although I haven't tested for W2003 Server).
Can't you guys see some wiley new guy adding a Users account (we're all used to seeing the Users group) to a bunch of PCs on the network after logging in with an Admin password so he can later do what he wants, even if security gets tighter?
Happy New Year, all!
Geoff