A standard practice is to have a UL element containing LI elements relating to each menu item
Each LI item contains an A element (a linkbutton is fine if you want to manage redirects or other functionality in code) Set the same text as your images, or whatever you want.
For non-CSS or aural broswers, your users now have appropriate menu access
OK - funky styling time.
Using CSS, set the style (and thus) background image for each A (or link button) to the default image. Set the text to be off-screen by altering the left margin to say -8000.
Set the css psuedo class ":hover" to display the mouse over image. You can also use a single double width image (with both the default and hover images side by side), and set the background image to the left for default, right for hover.
Most decent CSS books will have this and the "sliding doors" technique in for nice looking menu's
E.g. see "CSS Mastery" ISBN-13 pbk): 978-1-59059-614-2 availabe in the UK/US
If it was easy, everybody would be doing it.