Why convert, when they were already captured? Does not make sense.
Welcome to the forum.
Let's start with the basics. When you say "capture," exactly what are you doing here?
What is the model of that Sony camera? What format/CODEC does it shoot?
What is your Sequence Preset?
How are you converting, why and to exactly what "flavor" of AVI? This ARTICLE will give you some background on the AVI "wrapper."
As Harm says, if you are doing a Capture from the camera's miniDV tape via FireWire in PrPro, there is no need to convert to anything.
A link with many ideas about computer setup http://forums.adobe.com/thread/436215?tstart=0
Work through all of the steps (ideas) listed at http://ppro.wikia.com/wiki/Troubleshooting
If your problem isn't fixed after you follow all of the steps, report back with the DETAILS asked for in the questions at the end of the troubleshooting link
Do you have a USB drive hooked up to your computer?
First let me say that I have been fighting PrPro CS4 for about 4-5 days now, and only just started reading in here to figure out what i could do to "fix" my problem. I was having all sorts of fits with the playback inside of PrPro freezing and then "not responding." I came across all kinds of posts about computers, memory, drivers and settings, operating systems and all of that. It wasn't until some one that is also having struggles stated that they had a USB drive for unrelated storage did the light go on. So I disconnected my 2 USB drives (one a 250GB desktop Thermaltake drive and the other a 320GB WD My Passport) and loaded up a project that had all been rendered useless. VOLA, working like a charm now. Just like old times, I love my PrPro CS4, where about 2 hours ago I was ready to start working on my resume...lol
Bottom line, don't leave a USB drive hooked up.
Do not push me by plastering the same post allover the forum, please. Once is enough and appreciated, but all over the place just pushes it too far.
Cancel that, I am back to square one, well minus one really.