You never did mention the source of the video, all you said was avi and avi is just a container that can have many types of video inside it.
Also what is the output format desired (compress for the web, just viewing in iTunes)?
Any other information about the source video would help to design a workflow to minimize encoding time and maximize quality.
Some essential video properties to list (VLC or MPlayer should be used for avi to get their info) would be:
Video resolution: eg. 640x480
Runtime: eg. 45 min.
Video codec: eg. XviD, DivX, WMV
Audio codec: eg. mp3, aac, ac3