Alpha transparency? Is it possible?

[yostinso]

Hiya. I'm trying to make a skin for my college. I want to stick pics behind everything on the main window, but I don't want all the junk to cover them. I can make the buttons and sliders look okay by putting the pics I'm adding in the slider window (as in, draw a slider bar over the piece of my pic that it would normally cover). Unfortunately, I can't do this for buttons, cause they move.
Is there any way to make the buttons smaller or transparent? Maybe use alpha channel somehow? Or can the transparency definition file affect individual items?

Thanks,