Why do you want a lap for multiple monitor trading? The lap is far lessupgradable than desktop, usually significantly less powerful dollar for dollar, and impossibly a PIA to hook up additional monitors as you can see Use a desktop for trading and a lap for everything else.
If you want to connect mutli VGA monitors or multi hdmi monitors, you'd use a vga splitter or an hdmi splitter.
VGA splitter and HDMI splitter will project identical images on the additional monitor. I don't believe that's what the OP was asking. The OP was asking for each additional monitors displaying a different screen.
The setup Picaso posted looks pretty sweet, although expensive if one goes for the Apple screens as well. I`m looking at possibly picking up a MacBook Pro 15"-17" and set it up with one or two external monitors and use it as my trading computer. The MacBook Pro should be more than adequate in terms of performance, yes? My desktop is simply too heavy when travelling