Finally figured out how the Image List object works.
Seems you must have "use small icons" ticked, and it uses one image, with multiple textures, tiled width wise. Like so:
<img src="http://dl.dropbox.com/u/666516/mclist.png">
It does not accept an alpha, however you can set the List object background.
You must also link the Image List to the List object (the only object that uses it, as far as I can tell).
http://dl.dropbox.com/u/666516/list.cap
In the cap you'll see it automatically splits the image up into tiles based on the images original width, and the definable textures width, IE 224 divided by 32 equals 7 tiles.
The system is a bit buggy, image count is off, getwidth gives you height, same for getheight.
Then the list object doesn't accept clicks, and could use a few more expressions.
It does have some potential tho..., if you dont mind the quirks that go along with a Windows control.