Are you putting the files on as 'data' or are you trying to create a 'video dvd' to play in an external dvd player ?
If its the former then Toast should have no probs but mak esure the mac/pc you play it back on is able to understand the codecs properly - using vlc is probably best as it seems to cope with everything !!
... if its the latter you will need to convert the avi and mp4 files to mpeg2 to make a dvd ...
Gentall ... is that not a windows program ? AFAIK fizzgog is looking for a mac program to run ...
Why not just use iMovie & iDVD? My wife's stills camera outputs movies in avi and I have used iMovie to put these onto DVD. It should also handle mp4. Just import them all into iMovie, make the movie and export this to iDVD.