I have captured quite alot via my tv cards, converted a whole lot of vhs tapes to dvd that way.
Once its set up its easy as pie. Plug the 360 into the video in, you will need an av (female) to 3.5mm stereo jack to capture sound with it. Then its select the video in as the source, click record and you're off..
I have also recorded the odd tv series via that using the auto-tune feature on my dstv decoder, but I found the quality was not as good as the pvr or the downloaded series.... I'm keen to find a video capture device that accepts hdmi in, but I think that there are some issues with that...