Hi Doreen,
Sorry I forgot to mention the picture button is available if you are using InfoPath 2010. I'm afraid the only way to add the image to your button is to add it as a resource file and edit through XSL stylesheet.. Sorry, it's been a while since I've been on IP2007 - to export as source files, I think it's File > Export. Once you exported the source files, you have to look for the XSL stylesheet file, manually edit it. Example of adding a background image to button:
<font size="2"><input style="BORDER: none; BACKGROUND-IMAGE: url(ref.JPG); BACKGROUND-POSITION: center; BACKGROUND-REPEAT: no-repeat; WIDTH: 25px; HEIGHT: 25px" class="langFont" title="" value="" type="button" xd:xctname="Button" xd:CtrlId="CTRL1_5" tabIndex="0"/>