I know this is an ancient question, but since there's no answers and this is pretty much all that came up on google when searching for Zoho CRM integration with Google Maps I'll take a stab at this anyway. I recently got a similiar request, but in this case they wanted to display the leads on a page outside of Zoho.
I created a Java servlet and JSP that runs on Google App Engine. The servlet will connect to Zoho CRM to retrieve all leads and geocode the addresses they are registered with. The client-side Javascript is then taking care of creating the markers on the map for all the addresses.
It's a bit too much code to paste here (although not that much), but you can check it out at http://code.google.com/p/zohomap/.
I put the demo up at http://zohomap.appspot.com/.