this has started to happen to me lately. Not only in emule, but all other proggys as well. If I rightclick, most of the menu will be black, and only show up if I hold the pointer over each selection (like I've done with 'show comments' etc on this screenshot).
It shouldn't happen though, since I have 256mb ram on my vid card.
Rebooting will fix it, for a while anyway.
Damn annoying