If you haven't managed to work out how to do it or are a bit unsure. Try w*w.videohelp.com for tutorials and advice.
What I would suggest is that you use a program like MediaInfo to find out what codecs are used for both avi files, if they both the same you can use a freeware tool such as Virtual Dub (sourceforge) to join up the avi files. BTW you might need Virtual Dub Mod if the files are encoded with codecs such as xvid, divx, mp3, ac3 etc
Good luck!
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