for a while and using an arduino for a custom keybord decoder..ps2 and it works rater well..
in my new endever I have been working with ARINC-410 (phoenixcomm.wordpress.com) which is a 5 bit bus - negitive logic.. I also need 2 groups 3 bits for addressing, a read/write line (tri-state) and a strobe (data valid).
I would like to use a Arduino Duemilanove (but I have just ordered a Max, just in case i need more I/O), it has 14 digital I/O but I cant find any way to use some of them to read/write a parallel byte.. LOL Is the only way to get this in or out is to bit bang the dam thing?????? 
There has to be an easier way..
A little push please.. (in the right direction) 
Thanks
Cris
oh yes I am using 74LS125/6 for the databases, and 74LS237 for the 2 address buses.
You can use the analogue inputs as normal digital inputs or outputs.
Search for the direct port mapping link, to tell you how to get more than one bit to change at a time.
There is no 8 bit port free on the arduino. You could always use an I2C or an SPI port expander chip to get 16 bits parallel output.