There is a Windoze XP version of PT, these days, the performance should be as good as on a Mac. But, Steve isn't running the LE version that comes with the M-Box, 001, and 002s, the HD version costs 5 figures ($XX,XXX) just to get started. He also records guitars with real amps, loud, through mic'd cabinets, if that was what you are wondering.
Vai uses Pro Tools HD. As far as I know, it's Mac only becasue Pro Tools HD predominatenly uses its own hardware for audio processing where as LE uses your computers processor. That said, a Pro Tools HD rig (software + extensive Pro Tools hardware) quickly runs into five figures as mentioned above.
Additional processing cards $4995 each
192 i/o interface $3995
192 digital i/o interface $2495
96 i/o $2195
pro control $11995
control 24 $$7995
command 8 $1295
and all the plug ins can run into the thousands and thousands of dollars each. Pro Tolls is the stuff but its expensive.The software will not run without the hardware. Digi did this to combat piracy. There new digital live consoles are expensive also.