T'Bone posted a news item saying that Palpatine and Sidious are both played by Ian McDiarmid. This has been a point of speculation for some time, so it's good to see some spy address it. Chryen sent us the following note that seems to back up the notion (note it was sent earlier in the week):

This is Chyren here. In response to heated rumours on the Force.net Prequel Forum over the precise relation of Sidious to Senator Palpatine, I created this comparative image with the screenshots of Sidious and Palpatine from their action figure packaging, shots of the known Emperor from ROTJ, and blown up sections of their features for closer comparison.

http://www.jediknight.net/jkmag/bfp2/0compare1.gif

Notice that the shiny dragon clasp the Emperor wears at his neck is identical to that worn by Sidious.

I created this late on the 14th. Ironically on T'bone's Prequel Preview site, he later confirmed that McDiarmid is actually also playing Sidious. I stress that my image was created before this info was released, and was posted on both the Prequel Forum at your site and at The Virtual Edition's forum around 9.45 pm last nite.

So, as you see, a lot of people were all thinking along the same lines. It also makes sense if you look at other evidence. I mean, we've got names of every actor playing every character EXCEPT for Darth Sidious. Exploring the possibilities, I'll offer up another bit of speculation. Look at the Darth Sidious figure and the Senator Palpatine figure. Note how much more wrinkled Sidious is than Palpatine? If they are the same guy, why is one wrinkled by the Dark Side and the other not? Could it be that one is the clone of the other? After all, in the Dark Empire comic by Tom Vietch, the Emperor was resurrected as a clone. Before you snort and make cracks about what's canon and not, take note that Lucas himself approved Veitch making an Emperor clone. Not only that, Lucas reportedly told Veitch he loved the story. (Remember that Tales of the Jedi had a double bladed lightsaber first, as well.) Would that inspire a Sidious/Palpatine connection and make a good lead into the Clone Wars? Who knows! But it's fun to kick around ideas.