If you have some files that are MPEG-2, you should be able to load them into a DVD Authoring program like DVD-Lab or Sonic's MyDVD as long as they are within the DVD specs. This link can give more information on the compliant DVD resolutions. The audio should be at 48000 Kbps.
As far as AVI's go, you will need an encoder like TMPGEnc Plus to convert them to MPEG-2. After that, you could use an authoring program to author the MPEG-2 files to DVD.
Hope that helps.
Patrick