Phil,

To answer the general question first: If you have a sim that comes with a serial or parallel Tx lead; generally, that lead will only work with the specific sim.
eg my FMS printer lead only works with FMS, my Easyfly serial lead only works with Easyfly.

I also have the Ripmax RC Sim. This comes with a game port lead and a seperate Windows driver that allows you to use the Tx with any joystick driven game.

Now G2: I've got the USB interlink. When you start the sim, if you haven't got the interface plugged in the software won't start. Hence you have to use the interlink interface, you can't use a different lead.

To answer your question, plug in the interlink controller. After a coulple of seconds the USB light should start flashing. Then go to the control panel and select 'Game Controllers' (or whatever your version of Windows says'). If there is an entry in the game controller window then you should be able to use the interface as a USB joystick....