TV CAPTURE

I have WINTV card in computer and I capture TV with it but when I do it is very big file. It use about 2 gigabytes for every 50 seconds when capture as uncompressed AVI FILE. I want to capture files but smaller. Do you know what compression I should use work well. Is a freeware MPEG1 realtime compression can get for this card? My system is a duron 650 and 128mb ram and about 10 gigabytes free hard disk space.

--BooOOM--