C# - Get workgroup name

Question

Using Visual Studio 2010 - C#

I want to get the computers workgroup name.

I tried both of these on Windows XP:

string workgroupName = Environment.GetEnvironmentVariable("UserDomainName");

string workgroupName = (string)Registry.GetValue(key1, "Workgroup", null);

The first gives me the computer name.

The second is blank.

Please suggest a solution that will work on all versions of Windows.