First thing you have to do is Get Two Image of the exact same size then put them in the same directory of your webpage.
Second On the Webpage that your image are going on in the head seaction inside <> Type script language='javascript' the on the next lines do the following type < the input this staight after that !-- then on the next line type this temp1=new Image and on following line type this temp2=new Image then on the next line type this temp1.src="yourfirstimage.gif" then on the next line type this temp2.src="yoursecondimage.gif" then on the next line type this //--> then onnext line type this /script inside <> or go to view source and see how it is setup.
Third on Samepage as you did head section go to the body section of the docement make type < then type the letter a then type space then type href="thispagename.html" then type OnMouseOut="roll.src=temp1.src" then type OnMouseOver="roll.src=temp2.src" then type > then type < then type img then type a space then type src="firstimage.gif" name="roll" border="0"then type > then type /a in <> then you are complete.
Or you can just check source code of this page.
Or Copy code from textbox below and change image to your image.