I wouldn't bother with mining. Your computer would use more power than the amount you get. You will be competing with people who have custom hardware just for mining. At 700 MHash/s your net profit will be at least $-750 after the power bill.
You could of course buy a custom mining rig that would do about 60,000 MHash/s, about 4-5BC per day. The cost of the rig would be about $1,300.