More than one culture can have the same "name", but there are a lot of names to choose from. CultureInfo provides Name, DisplayName, EnglishName and NativeName properties. The culture Name property is the only unique identifier. The other names can be overridden by custom cultures, causing duplications. Those duplications aren't even necessarily errors.
For this reason, making lists of locales, such as a pick list for a user to choose from, shouldn't use the NativeName, DisplayName or EnglishName for a unique ID. This is why the Windows Vista Regional And Language Options control panel (intl.cpl) appends the .Name (ie: en-US) to the displayed names if duplications happen.
Code that depends on the uniqueness of the DisplayName, EnglishName, or NativeName properties will be broken by some custom cases and should be updated.
You can also look at http://blogs.msdn.com/shawnste/archive/2005/10/25/484811.aspx