there are a number of ways to 'record the screen'. One application is called Camtasia on a PC or CamTwist on a Macintosh. I can show you how to do this in the main PBL room, at lunchtime. What you will need to do is screen record a series of 'shots', then bring these 'clips' into iMovie and then add the voice over and sound effects - this is called post production.
Uploading textures is done from the file menu. You can search Google for 'textures second life upload', and this will give you a list of sites that will tell you how to do it. You then 'apply' one of these to an object you have created. You can look at Torley Lindens video tutorials on YouTube too.
What you need to do is outline what you intend to do, using a storyboard. This is just a sequence of still images (screen shots) that describe the main events in your movie. Then under these, indicate the dialogue that you are going to use. You will have that in your Social Studies work.
So post up your dialogue, then add your screen shots. We can look at this, talk about it and then you'll be ready to film. It will save you a lot of time and frustration later. The audio/voice will be added in iMovie right at the end.
So post up your ideas and dialogue. Great, sensible questions. See you Weds lunchtime!