If you are just stopping in Williamsburg on your way through you can walk through Colonial Williamsburg. This will give you a feel for the place. Buildings with flags require a ticket to enter. To truly experience CW you would need a ticket and 2 full days. A Bounce Ticket goes for about $100 and gets you unlimited admission to Colonial Wmsbg, Busch Gardens, and Water Country USA. It includes parking at BG and WCUSA. Children 5 and under can receive a free ticket. It's a fantastic value.
There's also a free ferry ride from Jamestown Island. Never done it but there's alot on Tripadviser about the experience.