You could combine the two images using a graphics program like Irfanview (free) or Photoshop, then make an image map which uses coordinates to create a link over part of the image.
See http://www.wickham43.net/imagemaps.php items 1 and 2a.
You would need to create a transparent gif for item 2a.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.