Of course we all purchased a Satio and are eager to create themes for it!
You too? Argh, Theme Creator 4.08 through 4.12 don't support Satio's Symbian OS yet. You might be interested in the following thread over at developer.sonyericsson.com.
For the moment we have to stick to Carbide.ui Theme Edition. read more here or in the Satio section at developer.symbian wiki
...without custom themes it already looks quite fine though!
(Update Feb 27, 2010)
A beta version is available for some days now.
Get the Beta Version 126.96.36.199 here http://creations.sonyericsson.com/download
You should read Gseth' comment before using it.
(Update May, 2010)
Sony Ericsson made a new Beta Release available on it's Developer World site. It's given version 4.16 for now and can create themes for Satio and Vivaz. For description and download link go here.