Well there is a software called qvm which can be used for
creating movie i.e an avi file from sequence of screenshots..
this sequence can be created from ac3d.
just google with the word qvm ( quake video maker ) you will
get the link to download the software. 8)
and if you did not like the above.. you could download
"fraps" a software ( shareware ) which enables you to create
an avi recording of what ever is done on the screen...
so that' pretty much it