Also, be careful with the front derailer - only shimano road derailers are designed to work properly with STI.
MTB derailers have a different geometry and therefore move the cage a different amount (for a similar length of cable pull) as an MTB changer.
So, when you get a front derailer, check with Shimano that it is STI compatible, and designed for smaller chainrings (as road cranksets traditionally have larger rings).
You can get MTB derailers to work "relatively" well with STI and MTB cranksets, but if you are not committed to a particular front derailer - contact Shimano and they will tell you the best derailer to use.
Persoanlly, there is a lot of mucking around to get it working - spend the $20 and get a derailer designed to work with STI and smaller chainrings!