1) Add new item-> bitmap (16x16). Set build Action=embedded resource (the bitmap will be buried in dll file)
2) Add the following attribute at head of control class:
' Specifies a type that indicates the assembly to search, and the name
' of an image resource to look for.
<ToolboxBitmap(GetType(MyControl), "MyControlBitmap")> Class MyControl
End Class
After the importing the control as dll from ADD REFERENCE..., in the toolbox I will find my control described with my icon.