HMMmmmm I am guessing you mean two separate (I ask this because there's a freeware filesplitting program called HJSplit that will split and rejoin files, but I have no idea if that will simply join discontiguous files).
For that just about any video editting program will do the job, because you would simply import one and the import the other and "splice" them together before saving..... Of course this may be a slightly resource intensive way to achieve what you require, but it will surely work. Also since you mentioned AVI as your format that is normally the chosen "raw" format for any editting - so should be compatible (though it is also the largest file format).
As to recommendations for a video edit program to do this job - well there are many threads already on that. In your case you'll probably want the most readily accessible freeware one I should guess - and unless you have one of those intro install CD's for something like "VideoWave" or whatever that commonly come with GFX cards etc. then I would guess M$ MovieMaker is the easiest for you to use... I forget how you get it, but I know it is free and I used it once and it seemed a cinch...
well yes they are from the net but they are totaly copyright free, they are in game videos from our clan site that we have made over the years and i just want to join them togther into one for the archive, we are redoing the site and all the content. i just want to keep them for later, join them into one.