Apologies - I was being stupid. I somehow missed the instructions about adding a new toolbar ad then adding items to it. But I still have a problem. When I go to "choose items" and hen browse to the toolkit dll, I get an error message:
There was an eroor loading types from assembly bla bla bla .... Request for the permission of type 'System.Web.AspNetHostingPermission, System, Version=2.0.0.0 ....' failed.
Why would this be?