x11vnc is the vnc server for the tablet, you don't need it if you want to control your laptop.

for that, get a vnc-server like tightvnc or realvnc, install it on your laptop, set up a password, and add the tablet to the list of allowed hosts (plenty of documentation for that available on the net).
then you fire up vncviewer on the tablet and connect to <your_laptops_ip>:0 (f.ex. 192.168.1.100:0)

":0" describes the screen you want to connect to, under *nix it's not uncommon to have several X Servers running, which would be adressed by :1, :2 and so on, but under windows there's usually only one, hence ":0".


for the other way round (controlling / viewing your N900's desktop from your laptop), it's basically the same.
you just fire up x11vnc on the tablet (the default setting is without password, and to close after one session, so you have to start x11vnc every time you want to connect, unless you set it up to start automatically, but then you also want a password, and it gets a bit more involved).
then use vncviewer on your laptop to connect to <N900_ip>:0, et voilà!

i use this regularly for sending SMS, works great!


for all of this to work, the laptop and the tablet have to be in the same network, of course! won't work over 3G.