Running video through an A/V receiver = problems = HELP!

Okay, I have a 28” Hanns.G monitor that has only one HDMI input. My PC has DVI output (or HDMI with an adapter) via two HD4870’s in crossfire – resolution set to 1920x1200. I also have AT&T U-verse HD television. I would like to view my U-verse and my PC video on this monitor (not simultaneously, of course).

My plan was to use my Yamaha RX-V465 A/V receiver as a switcher, running the U-verse into one HDMI input and my PC into another (PC via a DVI to HDMI cable), then connecting the HDMI output of the Yamaha to my monitor. Well, this works, but with one major flaw. When displaying the PC’s video, there is a black border all around the Windows desktop. Also, the resolution changes from 1920x1200 (16:10 ratio monitor) to 1920x1080. As a result, the display is then out of proportion (circles are ovals). I am frustrated as hell and hoping somebody has a solution or at least an explanation!