OK, so we all know it's completely impossible to inflate a real human body as it is with any lighter than air gas in the atmosphere of this planet to the extent that the person concerned will ever be more than a few grammes lighter than they started, so getting them to float in air is never going to happen, or for that matter even in a denser atmosphere because of the pressure on the body. That is the sad, stark truth.
However-
Whereas a person's entire body weighs tens to hundreds of kilogrammes, individual parts of that body weigh a lot less. The stomach, for instance, is a relatively light, thin-walled organ which will become appreciably lighter if inflated with helium, and the skin under the breasts. So whereas a person is never going to float, there is still hope, because it might still be that helium will make their breasts float, and even more so, make their stomach, intestines or the skin of their belly float, because those chambers are nowhere near as dense or heavy as their whole body taken as a whole. And this is a very, very good and hopeful thing because it means there are new possibilities with helium and hydrogen.
Just thought i'd float that one up there for you all.
Oh, by the way, before you go away with the thought that i'm talking about bits floating on their own, i'm not - i mean while they're still part of someone! I'm no Hannibal Lecter. Sorry, i suddenly thought that sounded a bit weird, even by the high standards set by this site.
http://www.youtube.com/user/nineteenthly