I don’t have to explain that it’s much better to use neat fancy images instead of regular html buttons. And sometimes designer succeeds himself and ads something really cool that you can’t simulate with CSS alone so background image for button should be set. On the other hand there is this stupid IE7 bug (afaik IE8 is ok) where you can’t see the background image for an input button if CSS border is set to “none”.

So this will NOT work:
<input type="button" name="button" value="Button" style="background-image:url(bg.png); border:none;" />

And this WILL work to display background image [also] on IE7:
<input type="button" name="button" value="Button" style="background-image:url(bg.png); border:0px;" />