HelpMouse related help needed

Ok, so, I have sorta added a draggable gui to a client. An issue is, that I have no idea what void or something I should call for the game to release the mouse, so I could use it to drag the gui. Ive looked at GuiChat and GuiIngameMenu but I cant seem to find anything.. :/ I think im just overcomplicating it for myself, but eh.. Any help appreciated.. ^_^

Uhm.. It might be the fact that im calling the void in a wrong place.. I dont know.. ;/