Hi,
Use
Gacutil.exe[
^]
gacutil /i dllpath.dll
At the Wikipedia page, you'll find the requirements for assemblies residing in the GAC:
Requirements
Assemblies residing in the GAC must adhere to a specific versioning scheme which allows for side-by-side execution of different code versions. Specifically, such assemblies must be strongly named.
But, as the others pointed out, you still have to add a reference to your assembly.