Create a group called "workstation admins" (or a name of your choosing), add all the user accounts to that group.
Either set a group policy, or individually go to each PC and add the "workstation admins" as local admins.
I'd prefer this method over setting all users as "Domain admins" or something, because there's no way you'd want all users to have full control of the domain. And this prevents them from having admin access to any servers.
There's probably a few more ways to accomplish this as well.