is there some way in properties of editcontrol to tell it that I actually want to add TAB "\t" to the editcontrol instead of changing focus on other controls?
If you're talking about a modal dialog (created using DialogBox) then it's not possible; the message loop handling the dialog responds to the tabs so even if you were to subclass the edit control, you couldn't get the tab key to just insert a tab char.
But you should be able to get the tab key to work with a modeless dialog. If you want it to act like a modal dialog you can disable its parent while it's active.
Or you could code your own version of the DialogBox function?