Grazing Cow Virus???

Ok, first let me preface this by saying that I'm not under the influence. I have this wierd thing happening with my system. I have a Dual 1.25 G4, running OS 10.2.5. I walk into work this morning and awake my sleeping computer to find a little animated cow eating a patch of grass on my desktop. As soon as I move the mouse to click on it, it appears shocked and scurries away. What gives?? Did I party way to hard this weekend, or is my computer under attack by some new kind of virus?? Anyone have any ideas what this is?

Cristian