Digital Speedometer 'layout'

im much more of a hardware nerd than software, and i plan on making a digital speedometer for my 1954 Vauxhall. im going to be taking the following general display layout from here:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1293959726

and whether i missed something or not, what it uses to read the rpm and convert it to a digital readout. i intend to use a photo-interupter (the one from jaycar: ZD-1901) but what im basically here for is more to ask how i would run the code (also taken from the above link) to register the speed, the code itself is 29,000 chars

to work with the hardware layout like in this link (see the bottom pictures):
http://www.8051projects.info/forum/showthread.php/579-digital-speedometer-with-8051-Microcontroller

p.s. i would like to generate a display accurate to 0.1Km/h and i have access to hightech milling and lave equiptment too, so theres not much thats out of the question

i intend to use a photo-interupter

Placed on what. Opto devices aren't normally very good for this sort of app because of the dirt under a vehicle.

read the rpm

RPM normally refers to the engine, I assume you are talking about a wheel or tail shaft.

the code itself is 29,000 chars

That's huge, I did a speedo with 6 trip meters in 7.5k (not Arduino though, raw AVR).

how i would run the code

Just plug it in and start making changes to match your application. If you copy the hardware there shouldn't be that ,many changes to make.

i would like to generate a display accurate to 0.1Km/h

I'd get something working first then look into that.

Rob