Hi erikgustaf, I just went through some of the replies in here, and I would like to point a few ideas:- using a motherboard
it is a very good idea, since it offers a lot of processing power, and no you don't need any special pins in it. To use a motherboard you simply need to have enough power for it, then the interface with the sensors and motors can be easily done using a microcontroller (like the atmega8) - this one communicates with the motherboard via the serial port, and it is not so difficult to build. then the microcontroller simply gathers sensor data and sends it to the motherboard, the motherboard does the processing and then send commands to the microcotnroller that triggers the motors accordingly.-power consumption
since you need to have this robot walking around your house, keep it mind that probably you'll want it to do this for more then a few minutes - so the mechanical design is very important since it might help you save or loose battery power. and because of the power consumption- you might have problems using e the mother board: I have a mini-itx motherboard with a celeron running at 1.3GHz, and it stays in the closet because I can't provide batteries big enough for it. So I'm considering using an ARM microcontroller that has the computing capabilities for handling video processing tasks.-microcontrollers
you can use instead a cheap atmel/microchip microcontroller like the atmega8 - for simple movement/sensor data will work nicely and the batteries will last long since it uses extra little power
(see this microcontroller board I've built: http://www.pocketmagic.net/?p=520
the design is important, since it can save a lot of power but also will be able or not to move where you want. I suggest big wheels, and geared motors.
Also you might want to make that a differential system since it will be able to turn around 360degrees.
Have a look on a design I've built from scratch recently: http://www.pocketmagic.net/?p=520
Move to the bottom to see my recent work. Also there you'll see some other ideas like using a remote computer to control the robot - this saves you with the powering the motherboard problem.
Good luck with your robot!