I don't know what do you mean when you say "except shell window".
First, the shell is one thing and the "window" (whatever window it is) is a completely different thing/process. Even more, if you have such a thing as a window then you are definitely not running just a couple of processes, because that means you are in X, which is probably run via a wrapper (xinit or whatever else) which also runs a window manager (or more likely, a desktop) which probably launches a couple dozen processes in the background. In any case, you definitely need init (the parent of all the processes) and also a given amount of daemons that are launched by init while booting your system.
At most, you could use "init 1" to go to runlevel 1, which will in turn kill *most* processes. That's the less you will get from a Linux OS while retaining some functionality unless you are ready to write a kernel module that can be used as a shell.
Last edited by i92guboj; 08-03-2010 at 03:06 AM.