I'm assuming your current account isn't called admin.
If so:
- go to system preferences > accounts
- setup a new administrator account.
- log out of your current account and into the new one.
- remove administrative privileges on the old one.
Keep in mind that this is generally a good thing to do, but it isn't as important as on Windows.
Each process is activated on its own, with its own privileges, and will require authentication even if you are logged in as an admin.
Of course this isn't true if you are logged in as sa in terminal.