Dan:
This has been beaten to death.
The tires are not out of balance. All tires can be dynamically and/or dimensionally out of round. There are two things you can do to reduce the problem. The first is to have the tires "trued" so that they are round. There are many shops around that provide the service. The second is to install a "rag joint". Almost all "street cars" have such a damper to reduce the shake to the steerting wheel.
www.allstates.com/tire_truing_machines.htm
Bob