Being as you've posted this in the HTML forum, I'll presume you've already got the graphics you want (normal, pressed and mouseover [optional]). In this case, you need to preload the images:
<script type="text/javascript">
(new Image()).src = "blogButton_normal.png";
(new Image()).src = "blogButton_mouseover.png";
(new Image()).src = "blogButton_pressed.png";
</script>Then, create the button like so:
<img
src="blogButton_normal.png"
onmouseover="this.src = 'blogButton_mouseover.png';"
onmouseout="this.src = 'blogButton_normal.png';"
onmousedown="this.src = 'blogButton_pressed.png';"
onmouseup="this.src = 'blogButton_normal.png';"
>Remove the mouseover and mouseout events if you don't want to use a hover effect.