If you want to extract an assembly (.dll) from the Global Assembly Cache you can use the following method which doesn't require a third party tool:

Open the Explorer and go to "Tools" in order to map a network drive.

There you can enter the server name and the folder: \\SERVERNAME\FOLDER. In my case it is: \\moss2007\c$\windows\assembly. You don't need to share the folder if you are an administrator. After the mapping you can browse the GAC and extract an assembly.