It's not terribly easy, but not terribly difficult. First, download and install x11vnc on your tablet. Now, on your computer, download and install pyvnc2swf (or some similar vnc recording program). Start x11vnc, and open up pyvnc2swf, and enjoy recording!
In my Mer/Ubuntu install on my tablet I used an application called recordMyDesktop.
You could search the debian armel repositories and experiment with manually installing the application from there, but I can't guarantee it'd work on Maemo.
I don't think the tablet is powerful enough to handle recording of the 800x480 screen in realtime.
Doing it with vnc2swf on a remote host should be a good choice.
