Totally Random

Well not really random - this is what I do for a living but I just cannot get this to work right and I don't know where I'm going wrong.

I want to make an image sprite using CSS. I've created the image I want - which is only an enabled state of a icon, and a disabled state and I want to show one or the other. I cannot get the stupid thing to work right. I found some tutorials on the web, but most of them assume I want to have an icon and a rollover state and that's not what I want. I know I will need javascript to test whether or not the button should be enabled/disabled - that is fine - it's just getting the 2 states to show up correctly I can't get to work.

I know the engineers can figure this out, but as the UI Designer I would like to hand off something that actually works right and they can use it (or not), but at least I got it right. ARGH! Help!