4:3 TV shows PC input as "widescreen"

My problem is that the output from my video card only shows up in the middle third of my TV, with black bars at the bottom and top, much like viewing a widescreen DVD on a 4:3 TV would look.

So here are the details: I'm using a eVGA Geforce 8800 GTS. The connection is a DVI to HDMI cable (DVI out of the card, HDMI into the TV). The TV is a Sony 4:3 HDTV.

Now I used to connect my PC to my TV using an S-Video cable and everything looked fine, except that there was a horizontal bar that slowly crept up the image, obviously some kind of signal noise. So I figured I'd try a different cable and use the HD aspect of my TV as well. But now the image is cropped to look like it's widescreen or something. Clearly that's not the case as my PC monitor is 4:3 as well, so there should be no problem.

I couldn't find anything in the TV settings or the nVidia control panel which seemed to relate to the problem, so I'm asking the forums for help.

Do yu have the resolution set to the resolution of the tv?

Not exactly. The only HDTV resolution that matches up with a PC monitor resolution is 480p. I tried 480p, 720p, and 1080i while my monitor was set to 1024x768. The space in which the image appeared on the TV stayed the same, it looked like at the lower resolutions it was displaying less of what was on the monitor. At 1080i I could almost see the entire contents of the monitor on the TV.