I agree, your 2nd option is good, although either will do the job. You really do want a
microcontroller to directly command the robot sensors and motors, rather than doing
it with the netbook, as you need a sense-motor loop with low latency for best control.
Also, it's much easier to hook up sensors to a microcontroller than netbook.
You will want to add some other sensors, like bumpers, sonars, Sharp GP2D12/etc IR
rangers. You probably need something lower than vision for direct sensing, as vision will
take a lot of work to implement. AFAICT, the computer vision problem really is not as well
solved as the advocates proclaim.
With the Arduino, there are several motor controller shields that will mount right on
the Arduino board, so you'll have a nice compact board arrangement. I think
pololu.com has a couple that will handle larger motor currents. I imagine with the
Lynx 4WD base you can run both motors on each side from a single h-bridge, but you
might check on that with the Lynxmotion people.
Lastly, another possibility to think about is adding RF comms to the robot, such as using
XBee. This way you can command the robot from your homebase PC and get status info
back while the robot is wandering. Eg, on top the Arduino motor shield, you can mount
an XBee shield.
One last thing, pay attention to how many I/O pins the various motor shields require. Some
of them eat up almost half the I/O lines on a regular Arduino 328 board.