You should only use Admin when you have to. Win2000 has a neat little feature called "Run As" which you should get aquainted with, it allows you to run stuff as any other user, such as Admin. If a trojan gets into your system, it will run with whatever permissions you are running with. If you are on as an admin, it can wipe out system stuff.
I don't even use Power User, as there is no point in my setup. All my stuff runs fine as a regular User. If I need other access, I can Run As an admin or a power user if need be.
I disabled a lot of programs under Admin just in case. I didn't even set up email, to avoid the temptation of actually reading mail when I am logged in for the brief times I need Admin.