There are actually two third-party plugins for Excel that let you use IronPython for scripting to some degree: DiscoveryScript at http://www.xefion.com/getting_started_diss.html and PyXLL at http://www.pyxll.com/ -- I don't use either, though, so I can't comment on how good they are.

(BTW thanks for the kind words about Resolver One -- that's my day job :-)