Your shifter cable is too tight. Set your front derailleur stops and then take a little tension off the cable. When I first started building bikes I made the same mistake more than once. If you have too much tension on the cable it binds up the shifter and it won't release properly.
A trick I use now is to turn the barrel adjuster all the way in, then back out one full turn. I then stretch the cable tight and tighten the bolt down on the derailleur. Once that's done, I'll screw the barrel adjuster back all the way in. That will put a little slack in the cable and allow you to downshift more freely. Fine tune your shifting with the barrel adjuster so that it picks up on the larger ring readily, but not too tight.
To set your front derailleur stops, shift the front into the small ring and the back into the largest cog. That should put your chain line all the way in closest to the bike. Then use the Low side adjuster screw and set the derailleur so that the chain neither falls off to the inside and doesn't rub and make noise on the cage. I usually shoot for about <2mm of gap between the cage and the chain. Then shift the front to the big ring, and the back to the smallest cog. That will put the chain line out furthest from the bike. Using the High side adjuster screw, set the derailleur so that the chain doesn't fall off to the outside and doesn't rub on the derailleur cage.
P.S. Tightening the adjuster screws moves the cage towards the rings, loosening the screw moves it away from the rings. Works like that for high and low.
Last edited by BFW; 08-14-09 at 09:16 PM.