Any tv tuner card you buy will support wide screen monitors. The max resolution you'll get for your tv signal will be whatever the service provider gives you...640*480 or 720*576 or whatever. When you maximise the application for viewing the program, the picture will be stretched, but you'll have black bars on the side. I'm currently running a Pinnacle PcTv 50i on a 22" widescreen LCD monitor. No issues. But all cards should be the same.
I actually wanted to get a Compro card, but I couldn't find one on the market when I was picking up mine. Its cheaper and better than the Pinnacles, so if you find one of those pick it up. Should be around 2k. I picked up my card almost 3 yrs back, so I don't know the current line ups, but back then the Compros seemed to have superior image quality. Personally, I don't like the pinnacle software much, though I like the fact that I've been able to customise the remote to use in a lot of my other applications.