Your question is kind of vague, what exactly are you talking about? Tips as in helpful pointers? By block you mean all of the "tips" in one container randomly displaying for a specified time, and then the next loads?
<div id="tipbox">
<p id="tips">
<?php
chooser=(rnd(1,2))
If (chooser==1) {
echo "Tip1 here."
}
else if (chooser==2) {
echo "Tip2 here."
}
end if
?>
</p>
</div>