Player 1 Player 2 Player 3 Player 4
Forward Up W I 4(NUMPAD)
Reverse Down S K 5(NUMPAD)
Turn Left Left A J 6(NUMPAD)
Turn Right Right D L 8(NUMPAD)
Fire Ctrl Spacebar Alt 0(NUMPAD)

Since the app is old and unsigned you need to add a Java security exception before it'll run, and it likely only runs in IE. To add the Java security exception open 'Java Console' go to the Security tab and add as an exception.