From the Quark web site:
http://www.quark.com/products/xpress...al%20licensing
QuarkXPress dual licensing
Can I install my single-user license of QuarkXPress? 6 software on another computer? If so, what is the process?
Yes. Dual licensing allows you to install your single-user license of QuarkXPress 6 on your secondary computer of the same platform. To activate dual licensing on the second computer, simply install QuarkXPress on that computer.
QuarkXPress dual licensing
I have one QuarkXPress 6 license, and I want to use a dual license on my laptop or home computer. Is that possible?
Yes, you can use a dual license on your secondary computer of the same platform provided that you are the primary user of the computers and you will use the dual license non-concurrently. A dual license is available only for one additional computer that you own. To activate dual licensing on the second computer, simply install QuarkXPress on that computer.
QuarkXPress dual licensing
How many dual licenses can I get? Can I obtain one for my laptop and one for my home computer?
You are eligible for one dual license per serial number, provided you are in compliance with the End User License Agreement.