Slow down there...
SpeedStep basically means that your processor runs at full speed when it's plugged into a wall outlet, but cuts it's speed (and power consumption) when it's running on battery.
Intel is learning from the overclockers again.
No, you can't build a laptop yourself. Well, you might be able to, but it's not worth the effort, and you can't really find cheaper parts.
You can upgrade them about the same amount as you can upgrage a M*c*nt*sh. RAM and processor.
And that's about everything I know about them.
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Apple? Macintosh? What are these strange words you speak?