PM me your e-mail address. I'll send you a workout book that is geared towards people like us who have a hard time gaining weight.
I gained 20 pounds of muscle in about 3 months with it.
Check out http://forum.bodybuilding.com When I first started working out that site was basically the pathway to my gains. I learned 50% of everything I know now from that site. The other 50 has came from personal experience and random other mags and sites. These guys here have listed some pretty good information. Right now you need to stick to basic movements and exercises that hit the most muscle groups at one time, and just eat like a freakin horse. I like to say, you don't eat because you are HUNGRY, you eat because it's TIME.
When I first started lifting 5 years ago I weighed just over 170 lbs. I have reached a peak about 2 years ago of 220 lbs, but right now I am stronger than ever and look bigger than ever and I weigh 205.