The wire library is used for I2C serial communications - have a look at this documentation which explains SDA etc
the code
#define _MRQ 4
.....and...
void MRQ_high(void)
{
PORTB &= ~(1<<_MRQ );
}
Is seting a particular pin on avr port B to 0 (which is odd given that it's called MRQ_high). I believe that it is equivalent to Arduino digital pin 12. See the port manipulation ref'd earlier and http://arduino.cc/en/Hacking/Atmega168Hardware
We could puzzle our way through all this but really, your best bet would be to poke around where you found the code and see if there's a connection diagram.
I'm interested in the project though. Can you show us the display? How will you get access to it?