Ok, I have looked plenty on selected states for buttons with CSS, there are many ways ranging from javascript to php, they’re all great tips, but when dealing with 5 to 10 pages websites a manual solution is easier:

Your CSS:
.selected {
background-image:url(img/button-selected.png);
background-repeat:no-repeat;
background-position: 50% 14px;
padding-bottom:15px;
}

Your XHTML:
<span class=”selected”><a href=”link”>Text</a></span>