why are some avi file have this oo1 or 002 behind them? and i can only play it in media player classic. for example: YUInamidairo.avi.001 what is that 001 mean? and how do you play the 002? i can't play it in classic media player.

usually the 001, 002 files are either RAR compressed files, or binary split files from HJSplit. You need to use one of these programs to combine back into one file.

You can probably try HJSplit first since that's what it looks like to me. It's a free program and just search for it on Google.