When I load RivaTuner it won't maximize the window, so I can't change any settings. I can get to it just fine, it's just not big enough to hit any of the buttons I'd like. I know this sounds really basic, but it's annoying. BTW, it was working before today....
Did you happen to change your Windows font size from the standard 96 DPI (if I remember correctly). In Win7, I think it corresponds to the "Control Panel\Appearance and Personalization\Display" setting of 100/125/150%. These settings can often cause issues like you are mentioning for applications that have a fixed window size like RivaTuner.
Check you are set at 32 bit color. Also what is your desktop res? That would be a request of mine is to be able to resize RT.