I'm thinking
select is a method,
checked is a property. Use the checked property (true/false) to determine the status of the radio button.
Not sure of the syntax but something like:
if radiobutton.checked = true then do something
if radiobutton.checked = false then do somethingelse
Does SharpDevelop have intellisense or auto-completion? That might prove helpful on listing the properties and methods for a radiobutton.