Eric Bana is a big star in Australia.
he played Hoot in Black Hawk Down.
for the hulk they scanned in his whole body and all the scenes where he turns big and green are CG version of his body, but they make it bigger.
all I know is that I read an article with one of the people from ILM and they said they scanned in Bana and they they just blew him up in the computer for the green scenes - I would assume that they used many bodybuilder's shapes as the reference while increasing his size - but they made it a point to say that they are basically just taking what they scanned and making it like his muscles got much larger.
Nah no way... I don't think having someone act as the Hulk would do him justice. In the cartoons we'd see the Hulk dwarf everything. I don't think ANYBODY is big enough to play the Hulk unless everyone else they cast is <5'7" and no more than 150lbs.