The first argument in form.Input (Checkbox is such an object) is the
name of the input, which is escaped because it becomes the
'name="foobar"' attribute, and could break your html if it wasn't
escaped. webpy also escapes the "description" attribute, which
defaults to the name value as well. There isn't an obvious way around
what you're looking for unfortunately.
You might have luck playing with the "pre" and "post" attributes,
which do not get escaped. Something like:
web.form.Checkbox('hello', pre='<a href="/">Hello</a>')
Hope that helps!
Cheers,
Justin