I agree that, if Obama gets the nomination, the media will try to portray him as moderate. The republican nominee will easily counter the liberal media with campaign literature, TV and radio commercials, and speeches which would tell about Obama's most liberal U.S. Senate votes. The Republican would also use that information during debates. The republican nominee will be conservative, but he won't be very conservative. Obama is very liberal, so the Republican will get more votes from independents.
It will be tough to portray Obama as a liberal when the GOP nominee could be an uber-RINO like Giuliani. The 2008 Presidential race could end up being a redux of Topinka vs Blago.