Some points:
Windows 7 is available in six different editions: Home Premium, Enterprise, Ultimate, Professional, Starter, and Home Basic.
Only Home Premium, Professional, and Ultimate are widely available at retail.
The other editions focus on other markets, such as the developing world or enterprise use.
Windows 7 Starter is only available pre-installed on netbooks, basic laptops, etc. You can't buy it on a disk.
Windows 7 Home Basic is available in "emerging markets", in 141 different countries in the "developing world". Some Windows Aero options are excluded. Home Basic, along with other editions sold in emerging markets, include geographical activation restriction, which requires users to activate Windows within a certain region or country.
Customization options are missing from Windows 7 Starter and Home Basic edition. For example you can’t change your wallpapers and there is no “Personalize” option in the Desktop context menu.
There are 3rd party software apps which are described as allowing personalization of Starter and Home Basic. One example is "Personalization Panel for Windows 7 Starter and Windows 7 Home Basic". Using this may involve applying a patch to a Windows system file, uxtheme.dll. Such a patch will be reversed by a repair install or possibly by a Windows update. As with all unofficial patches and modifications, it should be done only by persons prepared to fix any problems encountered, and ideally after making a system backup.