Was playing the computer for fun a few minutes ago and it jumped a pawn past my attacker. Does the computer have en passant rules applied or am I just retarded about en passant?

basically:

white pawn to F6, black counters with pawn's move to g5, and I cannot en passant capture the pawn, (no checks or anything)

You'd have to have been on f5, not f6 for en passant to apply (and the move to g5 would have to have been a two-square advance from black).

ah okay. thanks for the clarification.

Check the rules and basics under the learn menu.  There is a very good explanation of how En Passant works in the special moves section.

Correct and the capture fxg (f5xg6) would have to be on and only on White's next move after g7-g5 by Black.

It might help to think of it as a compensating rule for the pawn's special ability to move 2 ranks on the its fisrt move.