Got some arduino firmware coded up to strobe the switch matrix and send events back to a PC over USB, and some software on the PC to control everything at a higher level. Basing the software on pyprocgame (http://pyprocgame.pindev.org
), which is designed to interface with some proprietary pinball logic board replacement. The software is open source though, so I hacked in my own hardware layer.
Hooked the pinball playfield up to the arduino and tested out the switch matrix stuff last night. It works! Some of the switches on my old busted ebay playfield are dead (or the playfield wiring is broken), but it's good enough for now. Tonight I'm going to (finally) hook up the solenoid drivers. If all goes well and I don't cook anything, I should have a very primitive game playable this week.