Whenever you purchase a PC or lappy, most of the times the company tells you that this system comes with or preinstalled operating system win 7 or vista(or any other except DOS).
When you buy it from the local shop you get it preinstalled but nobody realizes that the dealer did not provide you any cd/dvd of the OS. Tell me one thing if company is using a single disc to install the operating system to the multiple systems(without different purchased license), it is piracy.
So the companies buy separate OS CD/dvds for separate systems(or sometimes use OEM for multiple systems, but only when preinstalled). And thus this CD is provided to you by the company. But, because you are not known to the fact, the local vendor/dealer hides it. And when the next time you will go to the dealer and ask for the genuine operating system CD he will sale you your piece, for which you have already paid the money. So first, check with the manufacturer.
For example I bought a Dell Studio with win7 directly from company(online) and got the win7 OS media, but for some low end Systems Company has mentioned on its site that OS preinstalled and OS media not included means OEM used by the company.
One more thing always ask for the Driver CD which comes with every system or motherboard.
Hope this will help.
Vicky