Slack is right about most TVs, but there are some newer models (not the HDTV stuff) that can handle 800 lines of resolution, and therefore can take 800x600 from a computer. I have a Voodoo3 with TV out and hook it up to the TV for some stuff, but the text is almost unreadable even at 800x600, and useless for anything but watching movies and playing some games. I would suggest getting a nicer monitor instead, 17" and 19" models aren't that expensive anymore. You would be better off, and your eyes would thank you for sure.
If you want TV out, check out the ATI card mentioned and the Voodoo3 3500. If you don't need the high end 3D acceleration then I have seen older cards still available that have TV out functionality, such as the Diamond Viper 4mb card, for about half the price of the newer stuff.