Carole says whenever she downloads TWiT netcasts in HD it stalls a lot. Leo says it's probably due to the age of Carole's PC that it's having trouble keeping up with the stream. If Carole prefers HD video, then a new PC may be her best choice. Or go back to the standard definition options.
If she's been streaming the HD and dealing with a lot of buffering, then downloading the video first is likely the best possible option. Streams like Netflix can't be downloaded because of copyright protection, though. Buffering is just the nature of the streaming beasts. If it buffers excessively, though, then that could be a bandwidth problem. It comes down to how much data she's getting, and how fast her internet connection is.