Stitching .avi files that are not compatible.

OK, first I'll admit that I really don't like movies a lot and I know little or nothing about film editing.
I should mention here that all of the following I did on a MacBook 6,2 with OS X 10.6.2
With that inauspicious start, I'll first refer to my last post where I found that Catenator is a great app for stitching .avi files but only those that were originally split from the same larger .avi.
It only seems to work if the files to be stitched have two extensions such as .avi.001 It won't stitch together .avi files.
However, I found this great thread that refers to quite a few apps, most of them free, which may do just what I want.
Only problem was, most of them didn't.
Now I had four .avi files which were all part of the same series of movies that I wanted to make into one, very long, film.
When I tried with both MPEG Streamclip and Split&Concat, I got only the audio from all four films concatenated.
With D-Vision, I got a file that looked about the right size (nearly 2 GB) but, although, the first and last of the .avis were included in the concatenated result, the second and third provided no video -- just a black screen.
It's only when I tried the same thing with Avidemux that and error message cropped up telling me that stitching was not possible because the files were coded differently.
Well, that's the first I knew about that.
Now it happens that D-Vision has a very nice, simple system to allow recoding of .avi files.
So I draged the first .avi to the D-Vision window and checked its coding. It was DX50 with a size of 608x348.
All three other files had different coding and size (mostly h264).
So I individually recoded all three avis to the same size and code with automatic cropping.
This took quite a while (typically 1 hour per GB of movie).
Next, I used the highly versatile D-Vision to join all four avis together in the order I wanted.
This worked perfectly which was very gratifying for a movie beginner like me.