A few of us SOs are dealing with that for the first time too... apparently it's better to take $87500 (or whatever the exemption is, prorated from how long you've been here) from your total earnings, and calculate the tax owed from that. I still haven't figured it out (I deferred my 2007 taxes until January 31, 2009), and I hope to find someone at CX with some answers too....
Reference:
http://www.irs.gov/faqs/faq13-7.html