You need to use a steering wheel removal tool. You can find these at just about any parts store from $15.00 to $100.00. Kragen's & O'Rileys will usually let you borrow one for free providing you pay the cost of the tool as a returnable deposit up front. again, that is usually around $15.00.
Here's a how-to page I put together to do exactly what you're trying to do:
http://www.64moneypit.pages.qpg.com/...cks/id108.html