I've had this problem since I bought a new PC. As soon as a pop-up comes up, the UI of Guild Wars disappears, everything of lotro disappears, etc. As soon as the popup is gone, the UI is back. I also have this problem with Google Chrome, so I just rarely used it. But some Litestep themes also seem to do this. Like Obsidian.

About those themes, I'm not sure if it's supposed to happen, but my desktop is completely empty, and there's no wallpaper. While Obisidian has this beautiful wallpaper in the screenshot, I just get the grey thing, with Litestep on it.

I'm pretty sure the problem lies with the ATI driver, but wanted to make sure about those themes first, before I start asking in other forums.

Anyone got an idea how to solve this? It's getting pretty annoying...

What pop-up? What is Guild Wars, what is lotro? What is the problem you have with Google Chrome, and how does any of it relate to LiteStep?

What do LiteStep theme's do that is a problem? Your description seemed to assume a pre-existing knowledge of your situation. You'll need to be more clear, or hope someone comes around that understands what you mean. :)