I don't have this set-up, but there have been a couple of posts here at BikeForums (I think in the touring forum) and I've seen some other stuff about this.

I'm assuming that when you say you want to put on a 10-speed mountain cassette you are talking about one of the new Shimano Dyna-drive (or whatever they call it) 10-speed mountain group.
As I understand it, this group is compatible with standard 10 speed road shifters, but you *must* use a 9-speed Shimano mountain rear derailleur. Shimano road shifters aren't compatible with the new 10 speed mountain derailleurs.
This this blog post here from a very good mechanic here in Seattle: http://bikehugger.com/2010/08/roadmtb-10sp-shimano-incompati.html

So the set-up would be:
- Shimano 10-speed road shifters
- Road compact double (or triple, for that matter)
- Shimano 9 speed MTB rear derailleur
- New Shimano 10 speed mountain cassette

Another option is to get a SRAM Apex rear derailleur, which can handle a 12-32 cassette w/a SRAM Apex rear deraillelur. I am pretty sure it's compatible with SRAM or Shimano shfiters.

As long as you are going down this road, if you want a "super compact" double you can look at the new Gran Cru crankset from Velo Orange which gives you a 46 big ring and a 30 small ring in the rear.
http://store.velo-orange.com/index.p...-crankset.html