dreadlocks?

Is there a way to get synthetic dreadlocks put on? Also, for dreads on natural hair, how is this done (say at a salon)& how long does it hold up? How often touchups be nessessary (at the salon) & would you have to do anything yourself to keep them neat? Is this costly? Also, I heard that for 3 weeks after being done you can't shampoo. Wouldn't the scalp get awfully oily?Jennifer