Last year, Microsoft sold the Windows 7 family pack for 2 months and discontinued it. Afterwards people were selling the software for more than what they paid for. This is because the family pack provides licenses for 3 PC's for only $150. The package includes 2 DVD's, the 32 bit and 64 bit version of Win 7 Home Premium.
The sales people at Microsoft store will tell you that this is an "upgrade" package, and that it'd only work if you install it over an existing version of Windows on your computer. This is not true, you can use it like a retail version disc and install on blank HDD.
The price of $150 for a 3-pack is a very good deal, because single PC license is over $100. There were a lot of people who horded the 3-pack and sold them for a profit last time, so I'd imagine there might be more people doing that this time around too.
This is a limited time offer/package from Microsoft. If you decide to buy it, you might be able to sell it next year at a profit. Make sure you keep the box shrink wrapped and new. Also, I think this package is not avail overseas in many countries.