> 1. OS timing problems- is it possible to just be rude and turn off
> interrupts while we run?

Not all OSs allow such things on normal programs, on DOS it is common
practice AFAIK.

> 2. If I remember right, there are some open collector outputs on the
> parallel port.

In theory yes, in practice most of them are just normal CMOS outputs. Most
modern boards since Intels TX chipset do only use 3V logic in the ISA bridge,
this includes the parallel port, so this is not a problem.

> Going the other way: when I hooked up the VMU to an analayzer, I used
> default TTL levels; so if my analyzer saw it's output levels, a parallel
> port should also see it.

3V logic is designed to be compatible with 5V inputs, as long as the inputs
are not on several harddisks by Seagate...