Usually, there's a minidisc size indention in the tray, if it's a slot load CD, you're probably out of luck.
I just picked up a PSX to USB adapter for dance pads, First I got a hvg2 from Frys.
Total fail. It treats the directional arrows as joysticks, so you can't press left and right at the same time.
Then I picked up an EMS USB2. It works, but not under Win764. The drivers won't load and you need them to be able to map the arrows to buttons properly.
The good thing is my cab is running Vista 32, and the drivers work fine there. Plus the company seems to be in process of making 64bit drivers.