What kind of video card are they installing, you want the best you can get so the aircraft will not only look better but it will fly "smoother" FPS (Frames Per Second).
If you are buying a new machine to run the sim get at least 1 gig of ram and if you plan on getting the next version of the sim make that 2 gigs.
As for the h/d I would go 60 or more, with today's bloated software you'll fill it up quickly.
A 1.7 gig will do the trick but you will have much better results over 2 gig, if you cut corners now it's not a desktop that can be upgraded easily.
Power is the keyword, this is a very graphic intensive piece of software.
Let us know what you do.