First of all, don't use the software that came with your STB card. Virtual dub can be found at http://www186.pair.com/vdub/index.html
and doesn't cost any money to download. You can capture an AVI using the PICVIDEO codec. You can select the PICVIDEO codec under the compression once you have entered capture mode.
Step One. Load Virtual DUB and enter capture AVI mode.
Step Two. Set all of your settings, including selecting capture multi-segmented AVI. You want to make sure to select frame rate and audio rate as well as the compression, screen size or any other parameter you want. Also select a capture file save area.
Step Three. Edit the video. You will need to use the de-interlace option in virtual dub if you are over 240 in vertical resolution.
Hope this helps. Let me know if you need any more help.