change background-image

change background-image

I've got a table of cells (duh) with unique background images and text in each. Upon hovering on any one of them, I need to change the background image to one named identically with the addition of "_on" before the extension (which is .jpg on all of them). And when hovering out that needs to reverse. I'm fairly new to jquery so I literally have no idea how I'd accomplish this (in jquery anyway, I could write the function I need in psuedocode). I'd like to accomplish this with one function, but I'd be perfectly fine with copy/pasting the same function into each cell tag if necessary.