1)
You might be able to download the Windows 7 Enterprise 90-day Trial from Microsoft.
Link – microsoft.com
2)
If you are ready to buy Windows, look for “System Builder” or “OEM” versions of Windows for the best price. However these versions are tied to one machine. Once you install and validate it, it will not validate on another machine.
If you want to be able to move to a new machine, buy the full retail version.
3)
The Home Premium version of Windows 7 is the cost-effective choice for most people, OEM is $99 US, full retail version is $189.99 US at Newegg.com (which is one of the best US sites for computer products).
The Home Premium download from Microsoft is $199 US
4)
Don’t buy a download (except directly from Microsoft). Don’t buy from someplace with a ridiculously low price. Don’t buy from eBay. There are lots of pirated versions out there, and it’s not fun when your copy of Windows says “This is not a valid copy, I will no longer work” and you can’t boot your machine. (Yes, it happened to me).
5)
If you need or want a new computer, then buying a new laptop with Win 7 installed makes sense.