Project - digital tacho

The winter is knocking, it's going to be a loong one, so I need to keep myself busy..

I decided to make a digital speedo, a idea crossed my mind when I smashed my buzzer this morning...i picked up the led display and thought - they! That would look cool in my car!

So I need some basic advices, tips, directions...

My car has a needle ona a tacho, and the tacho's cable goes into gearbox..so that's how it measures speed.

So, how can I make a speedo? 4 digit led display? Can I make a little sensor into the gearbox that monitors the speed, or maybe something near the wheels...I really don't know what's the easiest way, so please help.

The other thing is - refresh time. My friend has a car with digital speedo, and I really don't like it because it refreshes really slow, maybe every 1.5 secs or something like that...slow.

OK, after the speedo...is it a problem to make a rev counter, also digital...with a sweep effect?