Just a simple guide on joining an AVI using Virtual Dub, note both half's must be identical, you cannot join two files if they are different, like frame rate or frame size etc, as the join is done using streaming. If the AVI's are different you should edit one to match the other.

First load the first AVI


Now select File > Append > select your second AVI


Now save out the full AVI
Video > direct stream Copy
Audio > direct stream copy
SAVE AVI

Problems
Each movie half will contain key frames and delta frames, if the keyframe spacing is every 10 then there will be 10 delta frames KDDDDDDDDDK if the end of a movie has been cut at a delta frame, the join may cause a lip sync. If you get this problem, you would need to edit the end of part 1 and the start of part 2 so that they are cut at keyframes.