To make a screen.

I began with applying a texture on a flat, square prim that was reminiscent of white noise on a television.
Then I applied the following script in order to animate it to show movement on the screen:
default
{
state_entry()
{
llSetTextureAnim(ANIM_ON | LOOP | SMOOTH | ROTATE, ALL_SIDES,
1, 1, 1, 1, -0.025);
}
}
Layer this on top of a another flat prim (as your monitor) and add buttons wherever you would like in order to increase authenticity.