Well there are various ways of making a Second Life Movie, the following is just one way of doing so.
I will say that I’ve only had limited success with making SL movies, mostly because I think SL is aimed at Windows users and not Mac, so something I think is glitching some where along the line.
K to start you should Hide the interface, so it doesn’t show up in the movie you are making, less you don’t care in that case never mind the following step. Click Ctrl-Alt-1 to hide the UI so that it won’t appear in your movie.
Now to start SecondLife in making a movie, click Ctrl-Shift-A to start the movie (this command will also stop filming). When you first start up you will be asked where you wish to save the movie to, it is recomended that its not your desktop, but else where on your HD. Once you have chosen a place to save the video to, choose the video compression Full Frames/Uncompressed for the video, this will create a rather large video file (about 1 GB per minute, which you will be able to compress while editing it.
Thats it now recording of the video has begun, when finished hit Ctrl-Shift-A again to stop filming, open the video in your choice of video editor, such as iMovie and away you go.