How Can I Increase My Metabolism? (i.e. Eat Whatever I Want And Not Get Fat)

You need to eat about 25-35 grams of fibre daily & drink at least 8 glasses of water. This can be done by just making better food choices eg. Instead of regular breakfast cereal, eat something fibre rich like All bran (almost 14 grams per serve). Changes like this will increase your metabolism quickly & safely. Just read up more on the nutritional content of foods you like, you'll be able to work out a menu plan that you enjoy.

You don't want to!!
I eat 3000Calories most days, I can't gain weight to save my life and it's frustrating as hell!

I weigh about 150lbs.
Why would you WANT to be like that? It pisses me off, that all food products seem to be aimed at those who want to lose weight, yet those people like me, who find gaining weight extremely difficult, don't get any help at all. If you want to be like that then by all means but I personally wouldn't wish my metabolism on anyone.
Even if it is the digestive systems equivilent to a Maclaren F1.

Don't eat

Just stay as active as you are as you were before because the calories you burn should be more than what you take. Actually, I also wished that I could eat whatever I want and not gain weight. I was taking this brand of diet pills which won't let me gain weight regardless of what I eat because they have these ingredients which won't let my body absorb fats and too much sugar. It also increases my metabolism too. I have lost 20lbs in 5 months and now since it's not available in the market anymore, I'm starting to gain weight =(. You can ask your doctor which brand of diet pills would be best for you.