I assume Romney can win Indiana, and the entire south, including VA, NC, and FL, which seems possible. Then he needs Colorado which currently leans Romeny.
That's 257 electoral votes. Ohio with 18 then gives him the win. WIthout Ohio, it is going to be very hard to win because he would need to either win NV and IA and NH, Or win Pennsylvania.
http://www.270towin.com/