If you decide to have UAC on, right click on the shortcut, goto compatability, and check where it says 'Run this program as an administrator'.
Even though you may have an admin account, UAC prevents anything running with admin rights unless you specify this option. Turning off UAC as you have guessed, will run everything as admin as your account is so.
For any games running Punkbuster (multiplayer), it is generally advised to check the box I mentioned above, as this is what causes you to get kicked, or turn off UAC entirely. It's an issue with Punkbuster trying to scan RAM for cheating, but UAC not letting it. I think.