It's nice when the player dose not play to see a demo. You can do so with GE
You need to download and install FREE
LS maker
http://lsmaker.uw.hu/page.php
and
CamStudio
http://camstudio.org/
1. With your game playing use camstudio to record your gameplay
2. save.
3. Open it with LS Maker
4. It will create a serie of images.
5. In GE, create a actor
6. Put animation of those pictures.
The only thing missing is the sound. Maybe with realPlayer - you can convert into sound. Then you make both play at same time.
It can also be used to have a nice animated background. To make other stuff you can imagine.