A group of programmers have managed to create some Live Wallpapers for the N900. To get them, head over to the Maemo Garage and download the armtel.deb file for the latest release. As of writing this post, the latest release is 0.4.2.
Click here to download the deb file. Once this file is downloaded to your phone, use the file manager and head over to where you stored this and click on the deb file to start the installation. If you want to check out the wallpapers before you install this file, check the video below: