Let get some concept straight.
Are your images part of the content,or are they purely decorative? If they aren't icons or each image is different and related directly to the specific text...they are a content and you are better off using the IMG tag for BOTH.
If your images are merely dividers, icons or any such other decoration then a BG image is best. Do note that BG images DO NOT alter (make space for themselves) the content flow so you need to make the space for them using padding or margin methods.
UNLESS you intend to support ONLY CSS3, you can only put ONE background image per element. So, for example you will put the left image in the LI and the right image in the anchor.
ROUGHLY, something like this:
background: url(images/menu-item-default.gif) no-repeat 0 50% ;
padding-left: 20px; /* i assumed the image to be 10px so I added 10px to your padding*/
background: url(images/menu-item-default2.gif) no-repeat 100% 50% ;
padding-right: 20px; /* i assumed the image to be 10px so I added 10px to your padding*/
hope that helps.