A general rule for water crossings is if you can't walk through it, you shouldn't drive through it. Even slow moving water can sweep a car downriver pretty easily.

If you plan on doing this regularly, there are precautions you can take. There are techniques such as creating a bow wave to help drive through really deep water, and there are preventative measures you can do to keep your car from getting ruined. The air intake is only a part of the problem, you also have to worry about the vents on the axles, transmission and transfer case to keep water out of those areas. Then there's the whole issue with the electrical parts. A good 4x4 book will give you a much better explanation.

If you want to go through really deep water, get a diesel

http://youtube.com/watch?v=tzGh43-leO4

and if that's still not good enough, then you'll need a submarine