My question:

Is there a difference between a lead screw and a trapazoidal screw?? Or are they the same thing?

Trapezoidal usually refers to metric acme type screws.
A leadscrew can be any type of screw, but usually refers to higher precision screws specifically made for providing motion.

Just stumbled on this one, and a thought occurred to me: what's the metric equivalent of tpi? Or do you just measure an inch, then count the threads? I know this sounds stupid, but as I'm still new, could we chalk this up to ignorance coupled with inexperience? ;)

Metric thread descriptions use pitch not tpi. M6 x 1 is 6mm diameter 1mm pitch.

yeah metric uses pitch, which is the distance between 2 threads.

So, in a controller program (e.g. Mach), I'd set pitch instead of tpi?

Yes. Set the lead per revolution in actual distance.

Scott