AVI files converting to DVD

I have a mac mini(its got a g4 and osx).I have a dvd burner and have idvd ,imoviehd,roxio popcorn,and roxio toast titanium.I can burn movies that I own by using mac the ripper and then roxio popcorn(or toast,depending on the size).The AVI files that I download from the internet can be watched but not burned onto a dvd and watched in a dvd player.I know very little about this. What programs do I need and where can I find them?(I have downloaded alot of programs that say they can convert avi to dvd but they are always not compatible with mac).Please help me find a program to do this that works with MAC OSX or tell me how to do it with the programs I have if possible.

I find many apps to convert dvds into other formats, the only way I've seen, and it works,
is to use divx doctor 2 to convert the avi into a mov, then using quicktime pro or another app, convert the mov to a mpg of some sort, mpg 2 or 4, and you can burn that in toast under the video tab. divx doctor 2 can be found at versiontracker.com.
NOTE: you also need the divx codecs for quicktime which I think are also at versiontracker.com, or try 3ivx.com.

compression avi-dvd

i'm no expert, but have found that if i convert avi movie into divx using the divx converter, i then use toast 7 to burn to disc. tried this with toast 8 did not work. so if u want to compress and burn and u are as rubbish as me at understanding the complexities then do as i do. all files play back great on stand alone dvd player.