so i'm experimenting with 2 platforms for my next bot at the moment.
my requirements were that i wanted something with a USB host port so i could use a standard USB webcam for machine vision.
approach 1 uses a EPIA mini ITX motherboard and DC-DC converter. http://www.mini-itx.com/store/?c=2#p1641
with this sort of motherboard on the bot i would be able to get real time stereo vision working. (no more messy IR sensors for me....)
the main problem with using a PC motherboard is power draw.
using a less powerfull PC would obviously use less power but will still be hugely inefficient. PCs just aren't built with low power draw in mind.
using a 10Ah battery pack i was only able to power my MiniATX motherboard for about 4 hours, despite the motherboard only drawing around 1 Amp. (in theory it should have run for around 10 hours.)
i put this down to the battery pack only being able to supply that sort of high load near the top of it's charge cycle.
using a laptop motherboard would probably be a far more power efficient way of getting lots of on board processing power.
the other processor i am considering is a Linksys "slug". http://www.linksys.com/servlet/Satellite?c=L_Product_C2&childpagename=US%2FLayout&cid=1118334819312&pagename=Linksys%2FCommon%2FVisitorWrapper
it's designed as a network storage device but it's got 2 USB host ports on there, (with the ability to solder on another 2, as well as a standard serial port) and only draws a few hundred milliamp.
all you have to do is put a more usefull operating system on there: http://www.nslu2-linux.org/
and you have a small, powerfull processor, running linux, with USB, i2c, serial port, ethernet, etc.
this processor won't be powerfull enough to do real time stereo vision but will definitely be powerfull enough to do video edge detection and shape recognition from a single camera.
using something other than a microcontroller on you bot will mean you will have to solve the I/O problem. how do you read sensors and switch motors on and off from a standard PC?
i'm using this project to build USB I/O controllers: http://www.obdev.at/products/avrusb/index.html
so i'll still need microcontrollers on the bot even with my more advanced processor.
using a serial port or i2c I/O conroller is also an option.
i'm still undecided which processor i'm going to go with. (maybe i'll end up with 2 bots...)
while the PC motherboard is overkill, it lets you do lots of cool stuff with it's somewhat excessive processing power.
the linksys slug on the other hand is a nice compromise between power consumption, while still being able to use PC peripherals and operating system.
the advantage of using USB components and a standard operating system is i can develop the various pieces on my laptop and then plug them into the bot controller once they are working.
even the controller is changeable as they will both run the same linux operating system as my laptop.