Raider is right. The only two things I would add is this: eat fat-free as much as possible (think chicken, tuna, rice, noodles, etc.) and increase your workout to 2-3 hrs, 6 times a week. Yes, you heard me. Bulk doesn't come easy. You gotta spend time lifting. Less reps with heavier weights bulk up; higher reps with less weights cut-n-trim.
When I was bulking up, the first 45 mins was just a warmup! Bike, stairs, running...getting the hearbeat up and stretching was what it was about before I started lifting! Stretching is critical for muscle growth, btw. It might seem girlish, but it works!
It's a lot of work and dedication, but it DOES pay off!
Good luck!
