really depends on the video/audio quality you like. For 307kpbs wmv format, which is quite watchable when it comes to talk show or news or soup opera type, it takes about less than 150 Mb for 1 hr, 320x240 size. (horrible for sporting events, though)
I don't think you can directly capture TV show in divx format, but after processing, yes, it's quite common to make 700mb 2 hr movie CD.