Question about IEnumerable and IEnumerator

Thing that i don't understand is ex HybridDictionary implements the IEnumerable interface that have metod "IEnumerator GetEnumerator()"
But if you look at the class it implements only "IDictionaryEnumerator GetEnumerator();".
how come that it has an other return value than the interface and how can you do this yourself?
I tried to do my own interface that did derive from IEnumerable and retrun it in a function in the class, but it does't work.

//B4N WarWulf