Hi,

the N900 can output the Screen content via the delivered cable.
I want to know whether (and how) its possible to input touchscreen commands to the device without having to deal with a usb host etc.
Anyone done something like that already?

VNC might me a solution.

install x11vnc from the repositories on the N900.
install some vnc viewer on the computer.
then just enter the N900's ip and connect.

you can now use your computer mouse to controll N900

hope it is what you were looking for.

Iam looking for a way to input commands via uart or something,
as Iam looking to use an external touch screen monitor