Good idea I need it for a Gottlieb system 3 test fixture.

What ISA card do you need to run?
The card you need to run will come with drivers for a particular operating system.
If you need to run Windows XP then I would suggest a P3 or maybe a early model P4 (some oddball P4 boards MAY have ISA slots).
If the drivers are for Windows 95/98 then any P3 will be fine.
Suggest you go for XP though because Win98 is a total pig and although Win95C is better than Win98 drivers for the other peripherals can be hard to find.