Not really. The main problem is that your AVI-files probably are of a resolution _near_ a DVD's. Let's assume your AVI is 640 pixels wide, then Toast has to scale it with a factor of 1.125 (to 720px), which isn't really "good". You'd get better results by scaling _down_, of course. Then you have to see that both your AVI (probably DivX or XviD?) and the resulting MPEG-2 video are highly compressed formats, which means that some information is simply missing. In the original AVI you might sometimes see so-called JPEG-artefacts, mainly in darker areas. If you uncompress this and recompress it differently, you'll _always_ end up with an even lower quality, even if theoretically a DVD's MPEG-2 _is_ the better format. Transcoding, generally, is a bad idea.
I had the same problem. What did I do? I went out and bought a DivX-capable DVD player for almost nothing. (I believe it was around 50 dollars.) It plays most of the DivX and XviD AVIs I have. And I also save muuuuuch computer time. As well as money, because the AVI often fits on a CD-R, which is still cheaper than a DVD-R. Or I can pack more video on a DVD-R. Nice solution. I really, really hope that in a couple of years *ANY* cheap DVD player will simply _have_ DivX support.