There are two types of images available for N900. One that contains only open source software from MeeGo repositories and one that has some Nokia proprietary components installed.
The open image for N900 can be obtained from http://repo.meego.com/MeeGo/devel/n900/images/. There are four kind of files
The image with Nokia proprietary components can be loaded from here: http://tablets-dev.nokia.com/meego-codedrop.php
Note that you must own a N900 device and accept the Nokia End User License Agreement to access the files.
There are two kinds of files available
NB! You can use the open kernel with the closed image