Perfect Dark shares a few tidbits of information with us today:

One of the most critical aspects to Episode II is the reappearance of the Sith. Apparently since The Phantom Menace, some ten years ago now, the Sith have gone back into hiding. But that is all changing, as MACE WINDU fears to YODA:

Thanks for the report Miss Dark, here's a bit of speculation I (Josh) want to toss in as well:

So the Sith appear in The Phantom Menace for the first time in generations, then they go absolutely silent for 10 more years. Of course, that kind of happens when your plans are foiled and Darth Maul ends up split in two.

And just about the time the Jedi become confident the Sith have become extinct yet again, in reality it has just been enough time for a new apprentice to be trained and more forces to join with the separtist movement against and to exterminate the Jedi. Behold, Episode II.