Guys, can you offer any specific detail on what kind of I/O hardware you are using to interface the playfield electro mechanics with the PC?
Also what software is being used to build the actual game play rule set?

With the deterioration of old pin spares I wonder how hard it would be to replace buggered old controller boards with a PC running the show via D/A interfaces using something like Visual Pinball emu?

The driver board we are using was actually produced for that exact purpose - to interface between a PC running pinmame with a game for which there's no CPU. The project just seemed to disappear (maybe due to things like Parcal's wonderful CPU replacements making this sort of thing of little value?). We grabbed the last two boards, although Nug has speced a redesigned one anyway as it has some built-in issues and much of the componentry can be replaced with other less numerous components.

The OS is Windows XP - there's some stuff native to XP that assist with how Nug pulled this off, although he is looking at other options at the moment. The games rules are written in VB.