Im a little new to blender and I created a short (500 frames) animation. I renderd the first like 5 frames of the animation, then stopped it.Then checked just to make sure that it was working correctly, and it was. So then I renderd the whole thing, but as soon as I clicked on my video a message poped up saying " Windows cannot play the file. The player might not support the file type or might support the codec that was used to support the file" Do I need to dowload some codec for long animations, or should I not use AVI Raw? I just dont want to render 500 frames of stuff then at the end find out it doesnt work agian.
Thanks 
This comes up time and again. AviRaw is only there if you want to do any post processing in the compositor as it is lossless. You would then do the post process and output using a different codec.
Always render out as a lossless image sequence to prevent loss of data if blender crashes in the middle of a render. You can then output this as something like a quicktime or xvid movie that windows can play
From http://wiki.blender.org/index.php/Doc:Manual/Render/Output_Formats
Free Advice
Choosing which format to use depends on what you are going to do with the image. If you are going to
email it to your friends, use JPG
combine it with other images in post processing and simple color/alpha composition, use PNG
use nodes to simulate depth of field and blurring, use EXR
composite using Render Passes, such as the Vector pass, use Multilayer.
If you are animating a movie and are not going to do any post-processing or special effects on it, use either AVI-JPEG or AVI Codec and choose the XviD open codec. If you want to output your movie with sound that you have loaded into the VSE, use FFMPEG.
If you are going to do post-processing on your movie, it is best to use a frame set rendered as PNG images; if you only want one file, then choose AVI Raw. While AVI Raw is huge, it preserves the exact quality of output for the post-processing. After post-processing (compositing and/or sequencing), you can compress it down. You don’t want to post-process a compressed file, because the compression artifacts might throw off what you are trying to accomplish with the post-processing.
Note that rendering an animation long to calculate in a unique file (AVI or QuickTime) is more risky than in a set of static images: if a problem occurs while rendering, you have to re-render all from the beginning, while with static images, you can restart the rendering from the place (the frame) where the problem occurred!
Ok thanks alot that really helps