Yes, it will work. You'll need a mountain bike rear derailleur because the largest cog will likely be too large for the road derailleur to work without the upper pulley bumping into the large cog. Combined with your front gearing, either the GS or SGS mountain derailleurs should work. The SGS models have the longest cage, but since you're running a double crank, the GS models should work fine also. You'll also need a longer chain so it's long enough to cover the big ring/large cog combination (plus one inch)-
If you use a mountain bike cassette (32 tooth and up) you will need a mountain bike rear derailleur. I have done it to 2 bikes, a Surly Cross Check that I use for some light trail riding and a friend of mine's Cannondale. In both cases I replaced the Tiagra rear with a Deore rear, because of the pulley bumping well biked described. BTW both bikes shift as well with the Deore as they did before.
Last edited by ruppster; 01-12-08 at 04:42 PM.