Re: second screen
 

I can walk around. Carry BT keyboard in my hand to advance through slides.
Although there's enough BT gadgets with buttons on them, perhaps, say, a wiimote could be made to be a remote control for an N800.

Unless you mean presentations with more to them than just a slideshow, where you're actually doing stuff with the tablet, and want it on screen.
Then I'd use x11vnc on the N800, and some random VNC client on the PC connected to the projector, and walk around doing stuff.