heineken, here's the scoop.
Your computer has been discontinued four years ago and is out of warranty(obviously), so it took a little while to sweet talk the lady into giving out information.
That configuration shipped with the highest end processor that it would handle. You could take your chances and try an upgrade anyway, but I don't recommend wasting your money on a processor alone.
<edit> That's why the upgrade manual that I found for it does not discuss the upgrade of the processor. </edit>
<2edit> If you can afford it I would recommend replacing the PC. </2edit>