Minimum resultion on AVI->DVDr

[Mago]

What is the minimum resultion on a AVI file to get a resonble quality on a DVD after conversion???
I'm using AviSynth and CCE... I tried an AVI with the resultion 576x320. The AviSynth script looked like this:
AVISource("f:\output\test.avi")
BicubicResize(704,474)
AddBorders(8,3,8,3)
ConvertToYUY2()
The result was a anamorphic DVD with medium quality. I first thought it was some tweaking in CCE but I then found out that the resize wasn't very good. (I'm resizing almost 50 % verticaly)
So in the future I will try to find AVIs with higher reultion, so I don't have to resize so much. Or does anybody have any other good solution????

/Mago

[Mago]

Did some more tests and it turns out that the resize is doing a great job. The problem was the source, which wasn't very god. So how do i find a good AVI source that is ok to convert to m2v?
As it it seems, there are two factors that make up the quality on a divx movie, the resultion and the size (or bitrate, but they are linked). So a movie at 704xXXX that is 700 mb may not be as good as a 640xXXX at 700 mb. Due to this it can be very hard to find a good source if you can't watch it and then judge the quality...
Any good solutions???

/Mago