Banner geotargeting

Hi, I′m using wordpress 3.0.5 and my client wants to set some banners on the sidebar and footer, but he wants that there′s an option to set:

If user A is logging from Mexico City, then show him banner 1
if User B is logging from New York, then show him banner 2

and he wants that the site automatically detects from where the user is logging and then show him the appropiate banner.

Is there a way to do this??