You may want to hide every admin of your computer. Here is a Terminal-powered hint for doing it. Just open Terminal and type:
sudo defaults write /Library/Preferences/com.apple
After logging out of every admin account, it will take effect. Admins may show in the login windows if you called up the login window using Fast User Switching. To reverse, type:
sudo defaults write /Library/Preferences/com.apple
Do not delete the property! I tested it on Mac OS X 10.4, it may work on other versions.
To login into admin accounts, press down arrow, press option-return and enter user and password.