I want to buy Windows 7 licenses for the computers in my office. It has over 50 PCs.
So, what kind of license do I need to buy from Microsoft?
Microsoft Volume licensing is best for you , just select the region and order from here
The OEM license should be accepted when installing, but if you do not use OEM media then you will need to call Microsoft's activation hotline to complete the activation process.
Purchaser owns the license, but OEM licenses are not transferable between computers - they must stay on the computer they were sold with.
You can also go for individual copies( product key activated) for your company PC's - To obtain a new genuine Windows 7 product key, you'll need to buy an additional copy of the same edition of Windows 7, which contains a product key that you can use. For more information about how to get Windows 7 in your country or region, go to the Shop webpage. You can also purchase Windows 7 at retail locations.
Hope that helps
You need to 'audit' your computers to discover what you already have .. you also need to check how much RAM is installed (anything with less than 4Gb is likley too old to run Win7) - for typical 'office' use you will only need Win7 32 bit .. and talking of 'office' use don't forget you will need MS Office licences ... plus, of course, unless you are using Linux Servers you will also need Client Licences ..
Of course, all the computers will have been purchased with some sort of MS OS Licence, so for many you only need to pay for an 'upgrade' licence, HOWEVER as already pointed out, chances are Microsoft Volume Licensing will end up being the cheapest overall.
Windows 7 can be downloaded from MS official 'distribution partner' == Digital River' ...
Finally, with >50 PC's you REALLY SHOULD be employing a SysAdmin (if you are the SysAdmin, get the business owners to put you on a 'proper' course and get qualified MCSE or similar - because Licensing is just the tip of the ice-berg when if comes to maintaining a business system 'Domain' with'Active Directory' ..)
Keep OEM Licenses
If the PCs in your office have OEM licenses (stickers that indicate they are licensed with the copy of Windows 7 you wish to use), you can use those licenses. According to the EULA, the sticker on the machine must remain intact and you should keep receipts/invoices for the computers.
Be aware that there are certain networking restrctions on certain versions of Windows OEM products. Read the EULA for the versions you have installed to be sure you do not violate these restrictions.
You cannot transfer these licenses to another computer should you otherwise get rid of a PC with an OEM license. OEM licenses are married to the computer they are installed on and have an OEM sticker on.
Replace with OEM Licenses
You can purchase individual OEM licenses for the computer (using OEM System Builder licenses), but those licenses are tied to the machine they are installed on. You would need to purchase one license per PC.
Replace with Full Package Product Licenses
This is the least cost-effective option. You can purchase full copies of Windows 7 and replace the existing OEM licenses with them. According to the EULA, you must keep box the product packaging that the licenses come with, and documentation for proof of purchase.
If the PCs have OEM licenses but you wish to use a different version of Windows (for instance, they are licensed for Windows Vista or 7 Home Premium and you want 7 Professional), you can buy upgrade licenses to replace them. According to the EULA, you must use upgrade licenses to replace an existing legal OEM or retail installation, and keep proof of purchase documentation.
Volume License Agreement
Contrary to popular belief, this is usually not a cost effective solution, but it's an easy to maintain one. A volume license agreement with Microsoft allows you to purchase one license that allows up to a certain number of installations, provided that the installations are on a PC that already has an existing OEM or retail OS installed.
These licenses can be moved around and removed as long as you do not exceed the number of installations allowed by the agreement.
This is just my recommendation to you, but I manage the IT department of a company that is rapidly expanding, and it has become harder as time goes by to keep track of licensing. A volume license agreement takes care of this hassle, but regardless, a worthwile investment would be looking into an asset management software or database that will track your license usage and alert you if there are any compliance issues.
I use Spiceworks in my company and it does pretty well keeping track of things.