How to download Avi and VLC
First off, don't download AVI's of you can help it. Look for MKV's or MP4's.

Depending on the format of the video in the AVI you may be able to play it with the Perian plugin for QuickTime.

VLC is a good player and will play MKV and MP4 files, but if you still want to remove it you can just drag it to the trash. If you want to remove all of its corresponding files then download a free app called AppCleaner and use that to remove it.