Use this : https://dev.inigo-tech.com/svn/base/inigo.eventlocationmap/trunk/
A Five product for replacing Location field in ATEvent to a Google Map field
You will first need to deploy Products.Maps into your site first.
checkout the product into your buildout src directory::
svn co \
zcml = inigo.eventlocationmap
WARNING: this will break your existing event content, you need to migrate their location field to use longitude/latitude tuple
How to migrate? I'm still figuring it out myself.
Credits to Jarn AS for the excellent Products.Maps