Create Map mashup to show number of users per country

I have data on the number of users per country and I'd like this to be represented on a map of the world. I'm open to suggestions about how this is represented, I suggest using a 'heatmap' notion - ie. darker shade of colour where there is the most users. This can be produced using any mapping solution, but Google Maps would be a cool way of doing it. Solution must be viewable as web site. PHP can be used, but no other scripting languages or databases can be used.? Bonus points if you can make it so that the user can roll over countries and see a label with the country name and number of users. Data will most likely be in the form of CSV, with ISO country code in column A and number of users in column B.