Hi Dave and the rest of people having this problem.
The problem is with Windows XP. I have tried to fix this issue but it isn't as easy as it seems. It requires a complete redesign of ACDNR's graphical interface. For some reason that I can't figure out, nested group boxes (edge protection section) are being messed up on Windows XP, and nothing I've done so far seems to fix them. A quick and dirty solution would be putting everything in the edge protection section together without group boxes, but I haven't had the time to do that. I'll try to do it ASAP, but that's just a temporary fix specific to XP.
What I cannot understand is why when you switch to the Plastique style (Window > GUI Style > Plastique) it still doesn't work. The plastique style does not use Win XP's theme engine at all, so it should work exactly the same on all platforms. Have you really tried this?
On a side note, please realize that issues with Windows XP are becoming more and more numerous, and this situation won't get any better in the future. We are in fact thinking on changing our official support status for Windows XP, and we'll make some important decisions in this regard soon.