David,
The two drivers are EMI.SYS and EIQOS2.SYS
I just had opening Firefox for a second time in a session crash the system - black screen, no details, rebooted on its own. Never had that happen before. I've had Firefox disappear - which almost always appears to be related to something getting messed up in the profile - but never has FF taken anything else with it. So it looks like you are correct, and I just hadn't hit the issue yet.
So I will REM out those two drivers, leave the rest of Pen installed, and see what happens for a while. The popup keyboard, for example, still works without the drivers. Then I will try each driver one by one and see how that affects different Pen functions. I will also try the maxcpu=1 just for educational purposes.
Now that I have had Pen installed for a day or so and looked at its features, its value really is for a tablet PC, or perhaps for a convertable tablet/laptop used in tablet mode. For a digitizing tablet with its own driver hooked to a desktop or laptop that has a keyboard, not so much.