Can I download a design software like paint tool sai or photoshop on the iPad?

I like iPad's because they are very slim, portable, and I would be able to see what I am drawing on the screen unlike a wacom bamboo, which I was planning on buying. The cintiq would be better but I don't have enough money to buy one. Can I download paint tool sai, photoshop or any program like that on the iPad or is it too much for the iPad yet? please help me I really would like to try this out! ^.^