Dr.FOB - it depends on how much video you want on the disc. if you feel the quality is ok at an average video bitrate of 5000 (a.k.a. 5 Mb/s), then you can squeeze right at 90 minutes of video with PCM audio onto 1 DVDR... and have about 100 MB left of space on the disc. and from what i've read, it's a good idea to have a good 100 MB or so of "empty space" left on the disc, because some DVD burners have problems burning right to the edge of the disc.
if you want the optimal video quality go with 7000 to 7500 for the average video bitrate, and PCM audio. with the average video bitrate at 7000 and PCM audio, you can fit right at 69 minutes on 1 DVDR, and at great quality (where the DVDR quality is so well-preserved that it's tough to differentiate between the DV .AVI file and the DVDR). i've created several hundred DVDRs, and done side-by-side comparisons with the quality of the DVDR vs. original source (often VHS, or a DV cam source), and they look virtually identical. especially for a VHS source, it's extremely well preserved - and can often be even better than the VHS tape looks, if you learn a little and use some filters to "clean up" the video.