According to this blog, you can run DivX videos on the N97:
http://portablevideo.blogspot.com/2009/08/success-watching-avi-videos-on-n97.html
The DivX player is available from:
http://labs.divx.com/MobileDownload
The only thing is that because there is no "ctrl" function on the N97, you either have to use an external Bluetooth keyboard (as mentioned in the blog) or you have to use a program like Virtual-Key to reassign the keyboard for the application (as Steve Litchfield described as a workaround to running the old Mobireader S60 3rd edition software on the N97):
http://mobile.allaboutsymbian.com/news/item/10280_Mobipocket_reader_on_the_Nokia.php
Or another Keymapper as described in this thread:
http://www.allaboutsymbian.com/forum//forum/thread/88327/
I have not tried this yet as I am busy beta testing some software for Nokia (reported 4 faults and 2 suggestions this morning!).
There is a warning in the blog about not trying to watch too big of a video, but that smaller files playback well.