What is the code for having eg. a text/image link and when rolled over an image appears/changes somewhere else on the page? Thanks

A CSS way...
http://www.meyerweb.com/eric/css/edge/popups/demo2.html
Javascript way similar to what you want...
http://www.willmaster.com/possibilities/demo/doublerollover.shtml
Could also look through this page to see if your question is there...
http://developer.irt.org/script/image.htm