Windows 7 has 6 versions, but for most of users only need to decide between two versions: Home Premium(for general consumers) or Professional(for small businesses, remote workers). Features of each version explained:
Windows 7 Starter:
This is the bare-bones, 32-bit only version of Windows 7 intended for users in developing countries, to serve the most basic computing needs. Starter will not be available in retail stores, and will only be offered pre-installed on new PCs by Microsoft OEMs.
Windows 7 Home Basic:
Home Basic sits somewhere between Starter and Home Premium. It has all the features of Windows 7 Starter and will also only be available through OEM partners in developing countries. Also like Starter, it will not include the Aero Glass GUI.
Windows 7 Home Premium:
Windows 7 Home Premium has all the features of Starter and Home Basic and then some. This is the mainstream retail version that nearly all consumers will be using. Windows 7 Home Premium will be available worldwide to Microsoft OEMs and sold in retail stores loaded on new PCs.
Windows 7 Professional:
Also available worldwide, to OEMs and in retail, Windows 7 Professional has the features of Home Premium, but with added networking and data protection features for small businesses and those who frequently work at home.
Windows 7 Enterprise:
Windows 7 Enterprise is only available to businesses through volume licensing. It includes all the features of Windows 7 Professional plus more security and networking features.
Read detailed information here