My Mac Pro has a Dual-Core Intel Xeon 2.66 GHz.

Yes.

Any and all Mac Pro models can.

XEON Processor trumps Core anything Duo. You (and owners of ALL Mac Pro models) are covered for 10.7 Lion.

I have a Mac Pro

And when I go to the App store to purchase the upgrade it responds that it is not compatible with my computer. Any help here?

This thread was started before 10.8 Mountain Lion was available, and all questions and answers poted before yours refer ONLY to 10.7 Lion.

Your Mac Pro 1,1 from 2006 or so will NOT run 10.8 Mountain Lion.

But.... Lion is no longer available! odd. Got pulled. Anyone that had not (and I know people who can't run ML and now cannot upgrade to Lion --- or buy the usb thumb drive) which have been "pulled from the shelves." Guess Lion was taking up too much shelf space.

The hatter is correct that it was pulled. But this is to avoid people buying it by accident.

If you are certain 10.7 Lion is what you want, it appears you can CALL the Apple online store and they will arrange to sell it to you.

The same appears to be true of the 10.6.3 DVD. CALL the Apple online store to order.

http://store.apple.com/us/help/contact

Jst seemed odd and hasty to pull down any web page reference and hard to find tharpt you can, nay, have to call, for such purchases, hidden from view.

Should have put it online. And, when people called Wed, they were not aware or told and said, contact Amazon of all things! Which never sold thumb drive or Lion.

I agree it seems dumb.

And Apple does not seem to have adequately trained their people to the way you buy these items during 10.8 roll-out crunch.

We can only hope that they find a way so that folks do not buy older Mac OS X by accident, but that they can still buy if they know that is what they want.

You can still re-download if you bought 10.7 Lion before, it is just new purchases that have this added complexity.