Codec, Media Players and Movie Tools Help
Some movies require the proper codec to playback because they have been compressed to remain a smaller file. Movies with different extensions require a certain media player to play back. Below is a list that might help. You can also try to google for these

Codecs:
Official DivX 5.11 , get the codec only, not the player. It works with windows media player.
DivX Digest , a great site with many codecs including DivX 3.11 alpha & DivX 4.12.
Xvid codec , new codec becoming widely used.

Note: You'll be able to play 99% of AVI files with the above mentioned codecs installed. However you may still be missing a video codec or audio codec not listed here. You'll have to search google for the missing codecs.

Players:
Windows Media Player , your default player for MPEG, AVI & WMV files.
Quick Time , your default player for QT & MOV files.
Real Player , your default player for REAL files.

Note: Trouble playing WMV files? Then you need to update or upgrade your media player to the latest version. Even if you already have windows media player 9 you'll need to get the updates to play many of the WMV files online.

Tools:
G Spot , establishes what audio & video codecs are required to play your AVI files.
Movie Codec , a great web site featuring a wide array of codec & software downloads.

Joining & Editing Software:

J Fuse , joins & splits MPEG & AVI movie files.
Virtual Dub , easy to use editing software for MPEG & AVI files.

You can get movie making freeware from nonags, just do a search for what you want

Extra:

Spy Bot Search & Destroy , the best protection for surfing the web. These get rid of spy bots and such.

Spy Ware Blaster , another great protection software.
Ad Aware , another great protection software .