'98 Boxster base model "Christine?" Windows went down on their own while driving?
 

Driving along the freeway and the windows go down on their own all the way. When I push the buttons to make them go back up, they only go up 2/3...

Do I need an exorcist, or is there a mechanical explanation?

Probably one of the microswitches in the top latch mechanism is faulty, or the latch itself is broken. Typically happens when the car hits a bump. It signals the top control box that the latch is open hence it drops the windows.

Where should I buy a replacement micro switch?

Where are you? I'm in Walnut Creek area, east bay.

Ebay, Sunset Porsche, Pelican, etc. But first you need to identify the problem. Open the top and inspect the mechanism that operates the microswitches. When you press the small lever that the hook pushes upward when latching you need to hear two audible clicks. If you hear them try to keep your finger there and see if you can raise the windows. If it works that means that the switch is fine, just something is wrong with the mechanism.

I`m in Mountain view.

To me that sounds more like an alarm ecu problem. The alarm ecu is also the BCU in these cars.

Possible, I guess. Now that I`ve reread the post, looks like the window went down all the way. If it was the microswitch in the latch, the windows would go half way down only.