Looking at the specs for a 2005 silhouette, you have a shimano flatbar control group with an FD443 front derailleur. If you change to the drop bars and want to go with the STI shifters you will need any of the Shimano 9 speed STI brifter units and a new front derailleur from one of the 9 speed road groups, ie tiagra, or last generation 105 or ultegra. Your rear derailleur, crank, chain and 12/26 cassette will work fine. I think you already have road brakes as that would have been normal for the existing control group.