WMM codecs?

I'm really sorry if this is repetitive/brainless/etc. but i'm terribly confused and feel like i've searched around everywhere without any success.

Background Info:
- using Windows Movie Maker
- Windows XP
- the episodes i want to use are all on my computer (not on a DVD) through DC++ (peer-to-peer sharing network through my university) in .avi format
- never made a video before

My Dilemma
When i click File>Import Into Collections and click on the episode i'd like, it sends me this message:

The file C:\Documents and Settings\------------------\The Office\Season 3\The Office - 314 The Return.avi cannot be imported because the codec required to play the file is not installed on your computer. If you have already tried to download and install the codec, close and restart Windows Movie Maker, and then try to import the file again.

I don't understand what to do. I don't know what a codec is but after trying desperately to get some info, i just went on downloads.com and downloaded random codec packs that did not improve my situation at all. Please help!

[identity profile] yunafire.livejournal.com 2007-05-30 05:30 pm (UTC)(link)
You probably need divx, or xvid. Downloading something called 'G-Spot Codec', and it'll tell you what codecs a file uses/needs.
heresluck: (key)

[personal profile] heresluck 2007-05-30 05:53 pm (UTC)(link)
You might find http://www.videohelp.com/ useful; it's not about vidding specifically, but it includes a great deal of background information that it sounds like you might need. For example, the glossary includes explanations of codecs and of the XviD codec (as [livejournal.com profile] yuna_firerose pointed out, this is almost certainly the codec you need):

http://www.videohelp.com/glossary?C#Codec
http://www.videohelp.com/glossary?X#XviD

...and the tools section includes an explanation of and link to the GSpot program that [livejournal.com profile] yuna_firerose mentioned:

http://www.videohelp.com/tools/GSpot

[identity profile] darlulu.livejournal.com 2007-05-31 08:10 am (UTC)(link)
If you download the *full* version of the K-Lite codec pack here - http://www.free-codecs.com/K_Lite_Codec_Pack_download.htm - it should set you up as it covers most of the codecs (xvid, divx, etc) you'll need to import episodes into WMM. :)