Its a PRT-24x36. It may be either a standard or alpha. Post a photo of the stepper motor nameplate and someone on here will be able to give you that extra bit of information. It may have been referred to as a "desktop" when it was new. Now the desktop models refer to a different geometry.
That is a precursor of the BT-32 with a moving table.
My understanding is it should be able to run the current control software, but you would be well advised to call tech support and ask. Its a shopbot, so all the stuff we talk about here on the forum applies to that machine too.
Learn how to tweak it up for maximum performance from some of the other PRT operators on here, and you will be really glad you bought it!
Good luck- hope that helps.
D
"The best thing about building something new is either you succeed or learn something. Its a win-win situation."
--Greg Westbrook