To this, you first create your source icon, I assume using the stream returned by GetManifestResourceStream. I take it you're doing this already. You then use the following to extract the different sized icons from it:
iconLarge = New Icon(iconSource, New Size(32, 32))
iconSmall = New Icon(iconSource, New Size(16, 16))
iconLarge = new Icon(iconSource, new Size(32, 32));
iconSmall = new Icon(iconSource, new Size(16, 16));