May be 2 months too late, but look for a freeware program called Burn (recommended to me by a forum member). You can drag-and-drop multiple AVIs into it. It'll first convert them to mpeg-2. Then, you repeat with those and it'll generate one video_ts folder that contains all of your files. Note that AVIs are smaller sizes than the corresponding mpegs, so you'll need to make sure there's enough disc space on a DVD (4.7GB) to combine the files into a single folder.
I believe Burn is a frontend for ffmpegx, but it's much easier, cleaner (and smaller?) than the latter.