My intention is to use an Arduino Duemilanove (and eventually my own homebrewed clone) to replace the keyboard matrix of a 48k ZX Spectrum using the internal keyboard header in order to utilise a cheap and readily available ps2 keyboard.
The Spectrum keyboard is a 5x8 matrix (40 keys) with more detailed info here
I've seen something like this done with a microcontroller training board that uses a C8051F343 MCu here
. My guess (without properly researching it really) is that the ATMega328p doesn't have enough IO lines, I'd just like to stay with an environment that I'm comfortable with.