Hover question

[olsen]

I am trying to use the code for hovering on one item that then will show a larger image on another location. In the discussions a thumbnail is being used as the place to hover over.
I am working with a street map where I have coordinated circles instead (x , y and radius) and am looking for code to do that. It would be a bit like walking down a street and pointing left and right to see buildings. I am hoping for help to do this. Thanks in advance.
This is a CSS question, but I am new and don't know how to get it in the right place.