I'm aware of a bug in the Tau skirmish AI that practically makes playing against them meaningless. It happened in my copies of DC and SS, so I'm sure it's not an issue with the installation/disc. I also want it on record that I did do a search of this forum before and, and found no results. Here's the problems:
-Tau AI does not capture strategic points, relics, or critical locations. Because of this, they soon run dry and can't continue producing units.
-Tau AI doesn't attack or otherwise leave their base unless lured out.
-Tau AI only produces Tau commanders, vespids, stealth suits, kroot shapers, and battle suits (can't remember which ones)
This only happens in skirmish for both games. It's fine in the campaigns.