Mciahel is probably right about this. 350mb is a normal size for xvid or divx encoded tv shows.
Mpeg2, which is the only video codec allowed in dvd-video, is not as efficient in compression, so to maintain equivalent quality, you need to use a higher bitrate when converting. This leads to much bigger files sizes.
You can normally convert two 1hr tv programs encoded in xvid or divx over to mpeg2 and get them to fit onto a single layer dvd without too much loss of quality.