If I understand correctly, multiple pushpins show up on top of each other.

A couple suggestions:
How often do these records change? Could you get a unique lat/lon (i.e. pushpins shifted from center) for each one and store it with your data? Then you would map by the stored lat/lon.

You might also consider doing a shaded area map on code or a pie chart map with zip code.

Finally, you could program a custom rendering wizard for your data.. it would detect when there are duplicate zip codes and shift subsequent pushpins out in a pattern around the zip code center..

Eric

__________________