You likely haven't looked cause WYSIWYG editors suck.
Anyways, looking at the source code of that website, it's bad. College-trained web design hatred aside, what Vincent said is correct. The person who did that site made an image map with mouseover events, starting with the declaration of the image at line 14:
<td width="336"><img src="../mapasfe6/07.png" width="336" height="448" border="0" align="right" usemap="#Map" class="cursor"></td>
As a note, please never use tables (table, tr, td) for layout like this guy. That is seriously 1990's web design.
The map itself starts on line 130, and spans to line 169:
<map name="Map">
<area shape="rect" coords="272,351,289,367" onmouseover="Tip('Lv.7 | HP: 28, VA: 2<br>Po: 17, Hit: 69, Crit: 3<br>Eva: 8, Def: 12, Res: 0<br>- Javelin / Jabalina')" onmouseout="UnTip()">
<area shape="rect" coords="272,256,289,272" onmouseover="Tip('Lv.7 | HP: 28, VA: 2<br>Po: 17, Hit: 69, Crit: 3<br>Eva: 8, Def: 12, Res: 0<br>- Javelin / Jabalina')" onmouseout="UnTip()">
<!--Items omitted for brevity-->
<area shape="rect" coords="49,1,66,17" onmouseover="Tip('Lv.7 | HP: 19 (23), VA: 4 (6)<br>Po: 13 (15), Hit: 83 (90), Crit: 2 (3)<br>Eva: 13 (17), Def: 3, Res: 5 (7)<br>- Elfire')" onmouseout="UnTip()">
<area shape="rect" coords="112,1,129,17" onmouseover="Tip('Lv.7 | HP: 19 (23), VA: 5 (8)<br>Po: 10 (14), Hit: 88 (93), Crit: 7 (8)<br>Eva: 11 (19), Def: 3, Res: 5 (9)<br>- Thunder / Trueno')" onmouseout="UnTip()">
</map>
These lines define rectangle shapes based on the coords given in the coords attribute, in the x1,y1,x2,y2 pattern for the location of the first corner and opposite corner of the rectangle. It sets the onmouseover and onmouse out to two javascript functions.
The JS functions seem to be in some generic tool-tip library. It seems to be this library, but it hasn't been maintained since 2008, so I wouldn't recommend it for the sake of poor maintenance.
I'll write up a quick thing of what I would do for the situation. For simple tooltips, there's built-in HTML stuff for it, for more advanced stuff, a modern JS Script, like JQueryUI would be best.
Edit: Oh gods, I'm too lazy. Here's a plugin you can use. If you need help figuring it out, pm or email me or eat cheese: http://craigsworks.com/projects/qtip2/demos/#imagemap