i just did interviews/tests for the 2nd time round at prestwick a fortnight ago. like you i was concerned about the computer tests cos i couldn't remember them too well. as it turned out they were pretty simple and straightforward. below i've roughly summarised the 3 parts of the computer test. you probably remember them anyway and don't need this!
split up into 3 tests
1st test deals with coloured objects eg green diamond, red circle and ur asked to sort them according to the instructions before you as they appear onscreen. second half of test1 is about sorting numbers into groups eg the number 188 appears on the screen and u have to sort it by pressing A,B,C or D - in this example A=1-199 so thats what u would press.
2nd test is about ur spatial awareness. arrows appear onscreen with a dot situated to the left or right of it. the word LEFT or RIGHT will appear at the bottom of the screen. all u have to do is press YES or NO accordingly. the 2nd half of this mixes the first bit with inverted arrows ie opposite is true.
3rd test is the one where u get to stop all the numbers crashing into each other onscreen by pressing buttons. last part also chucks in some arithmetic too, but i think it's more about prioritising and avoiding collisions than getting 111*101 correct!
hope this is of some help and good luck.