Microsoft announced that "starting Oct 3 in the U.S., Windows 7 Family Pack will be available for purchase at participating retailers and online at Microsoft Store. Purchasing the Windows 7 Family Pack gives you three upgrade licenses of Windows 7 Home Premium fo $149.99. To take advantage of Family Pack, you'll need a PC capable of Windows 7 and running genuine copy of either Vista or XP". Win7 Upgrade Advisor can tell you which features and editions of Win7 will run on your computer(s).
So, don't delay. Windows 7 Family Pack will be available soon while supplies last.
For those outside U.S., Family Pack may be coming your way too. It goes on sale in Canada, UK, Germany, France, Australia and many other markets on or after Oct. 22 (Win7's 1 year anniversary!).
More Info: Microsoft Store