<p>How can I get a full list of Groups in my Active Directory?</p>

Microsoft .NET Framework provides a standard library for working with Active Directory:
System.DirectoryServices namespace
in the System.DirectoryServices.dll.
Microsoft recommends using two main classes from the System.DirectoryServices namespace:
DirectoryEntry
and
DirectorySearcher
. In most cases, it is enough to use DirectorySearcher class only.
You can find some examples in this
CodeProject article
.