ONE OF THE COOLEST THINGS that I enjoy about the Nokia N97 is its ability to play AVI files. You have to crank the AVI files through DIVX, using the mobile DIVX player here or HERE. Save the SISX file and install it onto your Nokia N97. It will install through the Applications Manager in the PC Suite or via the Ovi Suite. I also know you can copy the file onto the phone and run it from the file manager on the phone. You'll see the player on the phone and you can do fun things with it. Just load up AVI or DIVX files into the videos folder of your phone, run the DIVX Mobile App, and you're in business.
But if you have the Nokia keyboard at right, you're in for more fun because the keyboard lets you switch to full screen (best done with files that are 368x208) and change the movie settings for DIVX and XVID (AVI) files on your Nokia N97.
Knowing this, I'm starting to render files to SVCD (480x480) or lower resolution to avoid any playback issues on the phone.