Using your TV as a monitor should be as easy as powering down your computer, plugging the cable into your TV (depending on your TV, you can either directly use S-Video or get an S-Video to RCA converter), and powering your computer on again. You can adjust display settings for the TV through the NView control panel in your computer's display properties. Usually the quality of the display on your TV is significantly lower than that of a regular monitor, so you probably won't want to use it as your primary monitor.
As far as plugging your cable into your computer so you can watch TV on your monitor, that won't work unless your card supports VIVO (Video In/Video Out), which I don't think the Albatron 5700 Ultra does. Your other option is to buy a TV Tuner card such as the ATI TV Wonder, which you can find for quite cheap these days.