Paradog and tshdos were correct.

The file was in fact a asf file with an mpg extension.
I had to download the Windows Media Resource kit to analyse the file.

The asf file contains a script command that causes IE to go to a URL. That page contains the evil JS/seeker code.

Thank you for all your help.

If you have any thoughts on how I can safely play mpeg/mpg files please let me know.