Originally Posted by NoWhErE

2 - Every avi timeline is in its own comp right? Well create a comp whose length is the sum of all of the other timelines (ex : you got 3 timelines that are 30seconds each, well the new comp will be 90 sec) and bring the compositions into your new compostion and arrange them in the order you want. Then make a movie from that final Composition.

3 - Samething for your several .Mov you want to export into 1 avi, put them all in different comps and combine those comps into a larger comp. This process is called Nesting and is a VERY important process in After Effects. When creating animations etc, it speeds up your render time tremendously!