SomeNick, I see you have found the old thread/tutorial I posted a long time ago. (Eyeswater/Augenwasser= same )

There are a couple of things I would add to what was in the original thread which might prove helpful to you in your project.
For editing your fraps captures you should go get Virtualdub from here and if you dont already have Divx codec installed on your pc then get that here and use that codec for when you compress your raw video captures as it dramatically reduces file size without too much loss of quality.

I'm betting your brothers favourite flight sim is the IL2-Forgotten Battles-Pacific Fighters series
There is a Movie making sub forum on the Il2 site that has a wealth of information and whatnot over there

If you have any particular questions then ask away!
Look forward to seeing your movie