Here's a simpler solution but with no extra surrounding div:
<input type="submit" value="Submit">
The CSS uses a basic image replacement technique. For bonus points, it shows using an image sprite:
<style>
input[type="submit"] {
border: 0;
background: url('sprite.png') no-repeat -40px left;
text-indent: -9999em;
line-height:3000;
width: 50px;
height: 20px;
}
</style>
Source: http://work.arounds.org/issue/21/using-css-sprites-with-input-type-submit-buttons/