BCAA's are just 3 specific amino acids (Leucine, Isoleucine and Valine ) They are important because they are metabolized in the muscle and not in the liver. THey are absorbed the quickest at about 20mins from what I've read. Good reading about it at Invalid Link Removed
Protein powder comes from different sources (Milk, Whey, Soy, Hemp etc) and usually contains all the amino acids, and depending on the type has different properties like absorption time and growth fractions etc.