Micropat is the battery of pilot aptitude tests performed on the computer, hence the name. It usually consists of a number hand-eye coordination exercises using a joystick and/or rudder pedals, memory tests, spacial awareness tests etc. If you look out for WWW's big CEP posting in the Wannabes archive I imagine you'll find lots of information there which will help you.
BA use them at the first selection phase, as do the RAF, Cabair and BAE Systems for their airline selections as well. Oxford don't appear to, yet.
FF.