[alec.thomas]

Yea, this can be a little difficult I would reccommend doing what Ashley says. If not, what I did with our store is uploaded an image named btn_main_left.png and btn_main_right.png. Now if their different dimmensions you have to edit the css in the main.css file. you need to edit the height, width, and padding options below

button.button .button-right {
  display: block;
  background: transparent url(images/but_right.png) no-repeat right top;
  padding: 0px 11px 0px 0px;
  height: 22px;
}
button.button .button-left {
  display: block;
  margin: 0px;
  background: transparent url(images/but_left.png) no-repeat left top;
  padding: 0px 5px 0px 15px;
  vertical-align: middle;
  white-space: nowrap;
  font-family: verdana, arial, helvetica, sans-serif;
  color: #111d4d;
  font-weight: bold;
  font-size: 11px;
  height: 22px;
  line-height: 21px;
}