An Endnote license allows installation of the software on two computers. For additional installs suggest you contact “sales” for assistance in purchasing instead of purchasing the software online. By contacting sales you will be able to request and receive the three-installation license, installation instructions, and also obtain how to upgrade to Endnote X8 when the software is released(which may be free of charge for users who upgraded to Endnote X7 now).
BTW, if you are affiliated with an educational institution (college/university) you might check if your campus has a site license office which distributes software such as Endnote to faculty/staff/students at the educational price-rate.
Sales inquiries
call directly at 800.722.1227 or contact a distributor in your region
or submit a request http://endnote.com/buy/sales-information-request