The Student & Teacher Edition has the same functionality as the Standard
Edition. It includes three CD keys, so you could run it on three computers
simultaneously. However, this special deal is only available to qualified
educational users as defined by Microsoft:
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http://www.microsoft.com/mac/products/officex/howtobuy/howtobuy.aspx?pid=st
udentteacher&page=qualifiedUser>
In regard to functionality, the Standard Edition is identical to the Student
& Teacher Edition. It includes only one CD key, which means that it can be
installed on one desktop computer and one laptop computer, but the software
cannot be used simultaneously on both machines. You'd need to buy
additional copies of the Standard Edition to be able to install and run on
three computers. So, for example, if you had three desktops or three
laptops, you'd need three copies. If you had two desktops and a laptop or
two laptops and a desktop, and you did not need to run the software
simultaneously on all three, you would only need two copies.
The Professional Edition licensing is the same as that for the Standard
Edition. The only difference is that the Professional Edition includes a
copy of Microsoft Virtual PC 6.1, which is not included with either of the
other two editions.