How many oxygen does hemoglobin carries

In my book it states that "a hemoglobin molecule can transport four molecules of oxygen because each iron atom can combine reversibly with one molecule of oxygen" So does that mean Hemoglobin carries 4 oxygen including the oxygen in the molecule?

So another question is that where does the oxygen binds? Does it bind in the Heme with the Iron? Am I correct? :)

OHHH one more question: What about the Carbon Dioxide? I read from my book that it binds in the Globin rather than the heme group which makes it easier for gas exchange. But the carbon monoxide also binds in the Heme with the Iron which I don't get.. Someone please explain if I'm getting this concept right??

Thanks!

Hemoglobin has four heme-Fe centers (N4Fe) and each weakly binds O2 as nonlinear N4Fe-O-O units. As the first O2 is bound the hemoglobin expands and it becomes easier to bind the 2nd, 3rd, and 4th O2 molecules, hemoglobin literally breathes! Highly unusual kinetics. CO2 does not bind to Fe (no available low energy MOs). Carbon monoxide :C≡O: does have a lone pair and binds more strongly (~200X) to the Fe(II) centers of the hemes: Fe←C≡O (linear) and essentially you die of suffocation (Wikipedia must have carbon monoxide poisoning).
I've actually broke a rule and given you a website:
http://en.wikipedia.org/wiki/Hemoglobin