We've been giving cows milk for a few weeks now. At first, I was just offering it in sippy cups, but I have a hard time getting him to drink enough milk from them--he prefers to use them as projectiles! I give him cow's milk in a bottle in the morning and at night. We dropped the middle of the day bottle recently. I also offer milk in a sippy at other points during the day.
Do what works best for you. Right now, it is more important to me that he gets his milk in and using a cup wasn't accomplishing that. I figure that in the coming weeks/months, we will drop the morning bottle and then the nighttime one.