I also belong to the skinny brigade and can't gain weight. I'm between 6' and 6' 1" and weigh between 145-150 depending on the day. Would like to be about 170. I'm going to up my milk consumption and see if that makes a difference. I exercise regularly, running between 2-3 miles every other day. Have tried weights and protein mix in the past and they haven't made a difference. My diet is probably not too bad for a single guy. I try to limit myself to one fast food meal per week. Marie Callendar is my best friend.
For all looking to lose weight, try buying smaller cans of pop to slowly ween yourself off the stuff. I started buying the 12 ounce cans of Coke and have now moved down to the 7.5 ounce cans. Now when I have a 12 ounce can (which typically only happens when someone offers me one) it feels like I'm drinking a keg. Currently there is no pop in my fridge.
As an ectomorph, if you want to gain weight, you need to just eat more (protein in particular), and stop with the cardio.
Cardio just makes your body better at burning calories (while it burns them), which is NOT what you want it to do.
You are short-circuiting weight gain by burning those calories.
If I were in your shoes (and wanting to gain), I'd be eating a crap ton of fish, chicken, cottage cheese, dairy, etc, and chasing it down with protein shakes. Mix in weight training and you'll gain weight (muscle), eventually. If you don't care about what kind of weight you gain, just eat whatever you want. I know a guy who had to eat 8k calories a day just to gain. I think, personally, that would kinda stink, but that's what it took to gain weight.
Then again, if I was in your shoes, I might not be too upset about being able to eat whatever I want and not gain weight as well, and it would be AWESOME to be able to run with 60 less lbs on my legs. I saw that a rule of thumb was that you gained 2 seconds per mile for every lbs that you lost. 60 less lbs and I'd be getting close to a 4 minute mile! :biglaugh: