Haven't used vidomi in a while but if i remember correctly, when you are in video options and you can select the codec, select two pass divx networks, now there should be two buttons to configure. One for first pass, the other for the second pass. Be sure to enter the same bitrate for both passes. Now when you go to configure the first pass, set it under the type as two pass, first pass. Enter the bitrae and any other options you want.
Now for the second box (second pass) enter the same bitratw, but for the type click on two pass, second pass. Please note, the type should be in a drop down box.
Basically two-pass encoding, creates a log file for the first pass. It analyzes the video, the second pass is when it actually makes the avi file and it uses info from the log file to increase the quality and makes a better encode job.
All that one pass does it encode the video directly, it doesn't analyze it first, thus it is fasterm but in my opinion and many others' opinions, the increase in encoding time is well worth it.
Hope that helps you out.