If you see the latest release from Netenberg on Fantastico, you can see they have included the latest joomla (joomla 1.5.1).
...
So the problem here is that you haven't updated your version of fantastico, or you have forgotten to include this new joomla. Since they now support both joomla 1.0.14 and joomla 1.5.1. Joomla 1.5.1 is added as a "new" installer to fantastico.
*Sigh.* Step 1 has been done: Fantastico has picked up the new Joomla. Steps 2 and 3 have not yet happened.
Lunarpages does not pick and choose what's in the Fantastico section! Of course, you are always free to either upgrade your Joomla installation or uninstall it and manually install the desired version. In the former case, I can't promise that won't break future upgrades via Fantastico, and in the latter, Fantastico won't even realize that Joomla is installed.