hi.
well that won’t be tough. you just have to first clear the “Text For Previous Page” and “Text For Next Page” boxes in the admin panel, and then add a code in you css file for the following style:
.nextpostslink { background:url(your image url) no-repeat}
&
.previouspostslink { background:url(your image url) no-repeat}
“your image url” is the link t the image you wanna use. like : images/myimage.png
you should use the url WITHOUT quotes.
that’s all.