It is also doing that on 3 icons in the lower toolbar (home, something, and something)
I lost access to my XP machine for a bit.
I believe it to be a corrupt file. I don't know of any way to fix it.
I have had some odd things happen going from Vista to XP but nothing a little hair pulling couldn't fix. This problem is different.
The nav buttons and background work fine in IE7 on XP but they go black in windows explorer. The icons are black on 3 of the toolbar icons on XP but the other icons are fine. I have replaced images, added pixels, nothing works.