Upgrade from Mac OS X Leopard with Snow Leopard, a simpler, more powerful,
and more refined version of Mac OS X. It delivers a wide range of enhancements,
next-generation technologies, out-of-the-box support for Microsoft Exchange
Server, and new accessibility features.

It's the world's most advanced operating system, finely tuned from installation to shutdown.

Snow Leopard is an upgrade for Leopard users and requires a Mac with an Intel processor. About the Family Pack

The Family Pack Software License Agreement allows you to install and use one copy
of the Apple software on up to a maximum of five (5) Apple-labelled computers
at a time as long as those computers are located in the same household
and used by persons who occupy that household. By 'household' we mean a
person or persons who share the same housing unit such as a home, apartment,
mobile home, or condominium, including students who are primary residents
of that household but reside at a separate on-campus location.

This licence does not extend to business or commercial users.