My computer came with Vista and, of course, Media Center. I like Media Center, but I don't like the picture quality. My ISP is Comcast, and the picture quality on my TVs is excellent. I have no complaints about the bandwidth for e-mail, Internet, and all that. I suspect the problem is not with the incoming signal, but with either my video card or the monitor or both. Any suggestions of how to track down the source of the poor picture?

My system:
HP m7760n
Intel Core 2 CPU 6400 2.13 GHz
Windows Vista Home Premium SP1, 32-bit

My Sony digital flat-panel monitor (SDM-HS95P) connects to the computer via HD 15 cable (analog). The monitor has a DVI-D connector, and it shipped with a DVI cable, but my computer lacks a DVI port. I suppose it's reasonable to assume the connection between the computer and the monitor has something to do with the picture quality. Do you think upgrading the video card would measurably improve the picture quality? What else should I look for?