I've just saved this thread, I receive the same Spy Doctor ad.
I updated all of my SpyWare and Anti-Virus programs last night and since then I haven't seen it again. However, if I do I will Print Screen it for admin to look into.
I did notice a pattern to get an idea of when it appears, there's an ad at the top of the page that says " W I N N E R " in pink and green and flashes, this usually appeared before the Spy Doctor ad.
There is no way to close the ad either other than closing manually with Ctrl+Alt+Del as far as I know?!