You'd need the complete source code. They have an open source section, but only for various bits of the program, not the whole thing. To have a hope of making an OS X version, you need every source file for every bit of the program.
Then you need to either rewrite the interface in Carbon or Cocoa, probably the latter for speed, or include a version of
XFree86 to run it under.
Or you could get them to do it - after all, they probably want to sell it and make money, and they know the program better than anyone else. Have you asked them?
[This message has been edited by sadie (edited 02-28-2001).]