You might be wondering why on earth you'd want to do this, but it's trickier than it looks. I've published a gist for it. There's a couple of comments about how to get things set up as well.
The bad news is, RSpec works, but Cucumber doesn't. Instead I'm getting this:
can't convert Array into java::util::List (TypeError)
C:/Program Files/IronRuby 1.0v4/lib/ironruby/gems/1.8/gems/gherkin-2.0.2-universal-dotnet/lib/gherkin/native/ikvm.rb:37:in `new'
C:/Program Files/IronRuby 1.0v4/lib/ironruby/gems/1.8/gems/cucumber-0.8.3/bin/../lib/cucumber/cli/configuration.rb:29:in `parse!'
C:/Program Files/IronRuby 1.0v4/lib/ironruby/gems/1.8/gems/cucumber-0.8.3/bin/../lib/cucumber/cli/main.rb:94:in `configuration'
C:/Program Files/IronRuby 1.0v4/lib/ironruby/gems/1.8/gems/cucumber-0.8.3/bin/../lib/cucumber/cli/main.rb:43:in `execute!'
C:/Program Files/IronRuby 1.0v4/lib/ironruby/gems/1.8/gems/cucumber-0.8.3/bin/../lib/cucumber/cli/main.rb:25:in `execute'
C:/Program Files/IronRuby 1.0v4/lib/ironruby/gems/1.8/gems/cucumber-0.8.3/bin/cucumber:8
C:\Program Files\IronRuby 1.0v4\bin\cucumber:19:in `load'
C:\Program Files\IronRuby 1.0v4\bin\cucumber:19
Yes, you're reading the first line correctly. The downside of IKVM, of course, is Java Exceptions that mean nothing to you. This is quite frustrating for me, because I really wanted to start using Cucumber. So if anyone's managed to crack this, drop me a line. Believe me, I've tried enough different versions of the gherkin and cucumber gems to last a lifetime.
On the other hand, I'm rather enjoying RSpec.