Need help with formula involving dates

Hi,
I'm comparing two dates or ages (in days) based on dates. I want to get the difference in an integer form (number of days). I have tried using both IF and DATEDIF functions.
Problem is, the value comes out as a date. Sometime back in 1900, usually. Neat trick, that, but totally unhelpful.
Here's the one formula, which is not performing as advertised:
=DATEDIF(G4,TODAY(),"d")
where G4 represents a manually entered date like 4/1/2009.

Why is this happening? What can I do?