What kind of AVIs are you trying to put out?
If you click on your Sequence in the Project Bin, go to FILE ---- EXPORT ---- USING QUICKTIME CONVERSION
in the bottom left you'll see a QUICKTIME pulldown menu. Click on it and go find the AVI option. Then click on OPTIONS.
Play with the settings to get the AVI you need.
Keep in mind that MAC isn't a big fan of the AVI file format, so you might not be able to get the exact codec you're looking for (if its to show clients on their PCs I assume).
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I'm assuming you want to export your baby to DVD. Your best bet is to export your project using FILE ---- EXPORT ---- COMPRESSOR
and find the H264 DVD codec. Can't quite remember off the top of my head what the exact name was, but I believe its a preset. That will give you flawless DVD quality video
You can then import that file into DVD studio Pro and if you read the manual a bit, you'll be able to figure out what you need to do to get the results you want.