It will also invalidate the insurance policy, which will make the OP liable for any damage or injury he causes if the car is involved in an accident, even if it wasn't caused by the modifications.

See my previous post!

The maze will be illuminated, presumably, so ordinary light sensors should work.

The Mega328 in my Duemilanove can run at 20 MHz.

See the graphs around page 139. No one ever uses maximum ratings in their designs if they are sensible.

See the data sheet for the Tiny13A, it's 10 mA max.

An important difference is that the Tiny devices have much less drive capability on the outputs. I think it's only 5 mA or so, instead of 25 mA.

The Arduino can't be used as an 868 MHz radio receiver! You should be able to interface a suitable receiver to it, of course.

Check the soldering. It might simply be a bad joint.

A very good quality Duemilanove clone board I purchased doesn't mention Arduino on the board at all. I bought it from a UK supplier, but it came from here:

http://www.dfrobot.com/index.php?route=product/product&product_id=49

It clearly is a clone, from the description.

I'd use a DAC to provide the voltage to the regulator.

Have a look at the Vinculum chip, made by FTDI.

I've imported the Duemilanove Eagle PCB file into the Pulsonix software I use, and can view it in 3D. I can export it in the following formats: DXF, GenCAD and UniDAT, if that helps. For an accurate representation, 3D data will need to be added to the various parts; as it stands it uses a default height for them.

There is a Print command in the File menu.

The NXP TDA7052 is a modern device, and much better than the 30 year old LM386.