Viewdemo XXX, starmovie XXX 90, endmovie, take screenshot from folder cstrike and use virtualdub to render them into movie. Then viewdemo XXX, and record sound of the action with program Total recorder. You're welcome.
but it doesn't' convert .dem files into .avi files etc. you have to use the command startmovie, or hlae in order to get .bmp files which then are converted into .avi files.