Recording analog TV actually requires a beefy computer because it has to encode the analog signal into a digital file, usually MPEG-2, on-the-fly. If your CPU isn't up to snuff, or your are using the computer while recording, even just for display, that could easily result in choppiness. Digital recording is actually much simpler because it's simply recording the same stream of 1's and 0's it is receiving.
That said, you can get around the analog problem by getting a tuner with a built-in hardware encoder. This takes the load off of your CPU and passes it to silicon especially dedicated to the purpose. An EyeTV250Plus has a hardware encoder. It should do the trick and improve your analog recordings.