Sorry, shankar, perhaps I should have explained that my html/css knowledge is a little lacking. I figured out how to give the buttom image a class name and position it using css, but the old-age problem of getting it to align properly in all browsers arose. I got it lined up in FF, but it's slightly out in IE - as for how it looks in the ever-growing range of other browsers I dread to think. I found a site which described displaying the search box and button as one image, so that it would be lined up in whatever browser it was viewed in, but the instructions were beyond me.
For what it's worth, this is how it currently looks (although I'm constantly working on it so it could look like anything at any given time)