Need help with AVI video files!

Hi everyone.

Someone please help me. I'm trying to play an AVI video file I downloaded, but when I open it up in QuickTime, it tells me I need additional software to play the video, and brings me to the QuickTime components page on the Apple website. There doesn't seem to be anything helpful there, so I tried looking for a video file converter. So far, I haven't found anything that's free and that works right. Does anyone have any tips or suggestions?

Thanks!

P.S: This is on a Mac, not a PC. And I also don't have the latest version of QuickTime, but the one that comes installed on Leopard.

Please search, this has been discussed many, many, many times.