Originally Posted by michaaa62

The .deb files are packages for Debian based linux systems like the Nokia N900. They are compiled for quite some computing architectures, one of them is armel. You will only install packages for the armel architecture on your N900. The application to install .deb packages is called dpkg.
Sometimes the postinstall configuration of a .deb is not possible because of missing dependencies.
Most of the time the more advanced apt-get is able to install the missing packages.
One prerequisite to work with dpkg and apt-get in X-Terminal is a working root login. For this to work you should have rootsh from extras repository installed. Then

Code:

sudo gainroot
dpkg -i PathToYourPackageFolderHere/*.deb
apt-get install -f

will install all of the .deb packages that are contained in the folder PathToYourPackageFolderHere.
Any questions? Feel free to ask here!