Pro Tools is a hardware/software combination.
There is a cut-down version Pro Tools LE, 24 tracks max and comes with the Digi 001, or the Mbox. It uses your cpu for all efx processing. and mere mortals can afford a LE system
Then there are fullblown Pro Tools systems that start around $7000. They have dedicated DSP cards, and interfaces. The computer is really just used for a visual interface, all efx processing is done by the DSP cards.
If you are a business a fullblown PT system is a client magnet.
PT can run on windows or mac. On PC full PT sytems, have hardware requirements that are very tight, and most off the shelf machines won't work. LE systems are more forgiving.
I'm running Cubase, and DP3 on a G4. DP3 has OMF import and export, so I can interface with large PT studios.
Go out to their site and download PTFree to see if you like it.
It has sparse midi features, I prefer Cubase and DP3 for their versititlty.
Don't know why there isn't a PT forum, there are plenty of LE systems out there on both platforms.