wholemilk,
Use the Dashboard Interface + (Manage Widgets...) button to deactivate/delete the widgets that you desire to remove.
Depending upon where the widgets are installed, you may see a white line inside a red circle icon next to the name of the widget. If you click on that icon you will be given the opportunity to move that widget to the trash.
Widgets installed in the Macintosh HD/Users/yourusername/Library/Widgets folder will use that method for removal.
Widgets installed in the Macintosh HD/Library/Widgets folder will not have that icon and should first be unchecked. Then go to the Macintosh HD/Library/Widgets folder and drag the widget to the trash. You will be required to authenticate as as user with administrative privileges in order for the widget to be trashed.
and while I'm at it the calculator that automatically opens every time I hold the button on the mouse.
Are you sure that a widget which is controlling that behavior?
You might want to check your System Preferences...>Keyboard & Mouse>Mouse for deactivating that feature.
;~)
