In Inkscape 0.46+devel, built Jul 16 2008, on Windows 2000, the Node tool is broken:

You can't select the type of node at all if no handles are shown on the node. (i.e. select a newly drawn node and apply a type to it).

When handles have been dragged out of the node, then you can select the node type in the toolbar.

This is a change of behaviour from before.