Like harley posted, there are many apps for editing (cutting, trimming) video files.
The [B]videohelp[/B] website has a list of many to choose from.
For avi files, recently I have been using AviDemux with good results, but the UI is takes a little time to work out if you are a new hand to editing video files. There is a new version of AviDemux out now.
Keep trying out different programs until you find one you like.