I have an "icon" in my Windows (XP, if it matters) notification area (by the clock) which renders no image, but rather an empty square space (no borders -- nothing rendered at all in the space where you'd expect an icon). Upon mousing over this space, it immediately collapses (disappears), preventing me from gathering any information about it.

I'm assuming the collapse (on mouseover) indicates the process is no longer running.

How can I learn what process is painting this "void" in my notification area? I don't control the workstation, so I can't control what launches when.