The Windows Contextmenu

Could some please tell me how or point me to a tutorial on adding ''folders'' to the windows contextmenu. Like 7-zip has done:

I understand that you have to make changes in the registry although i am unsure on what i should be changing, i can successfully edit the registry to display a file on the contextmenu, although that is only 1file and not a folder full of them,

I would appreciate any help i can get on this matter,

P.s. im using Visual C# 2005 Express Edition