Will it be easy to write event handlers for DOM events and manipulate DOM in python?
update: This is an old answer, nowadays you want to go with an embedded browser in your app (*webkit projects etc.), but at the time of writing, no such technology existed. The answer is still valid if you don't want to add quite a few megabytes to your packaged app though.
Find a lightweight server, or better - embed one in Your application. That's it.
Java has classes for serving http. Python does it well also.
See how mercurial's hg serve works. [python]
I once did a tiny app that served aspell spellcheck via http on localhost in java with the httprequest class. [worked on win and linux]
Create Your application as a server that outputs some html and uses POST to do actions. Do the interface thing in HTML+CSS+JS. Nice and easy.
After running point the user to localhost:somesillyport or trigger opening localhost:somesillyport in a browser.