I needed to set the UID for an account on my Mac OS X 10.6 (Snow Leopard) box. Various posts online said that you can right click on an account in System Preferences -> Accounts to access the Advanced Options. But right clicking wasn't doing anything for me. Finally I tried a Ctrl-click, the standard way to "right click" when you only have a one button mouse, and that worked. My right button works everywhere else, but for some reason in this instance it didn't.