Auto creation of case from opporunity/potential 'closed won'

Auto creation of case from opporunity/potential 'closed won'

Hi all,
 
Does anyone know of a way of having a case created automatically when an opporunity / potential is 'closed won'?
 
We are a service company and an opportunity is always a job of some description (it may be a repair, installation, maintenance visit etc).  When the customer accepts our quote, we have to open the opportunity, change the stage to closed won (in order to register the sale) and then manually create a case for the job which essentially requires pretty much the same key details inputting as we logged in the opportunity.
 
If a case could be automatically created simply by closing an opportunity as 'won', this would save us this seemingly pointless double-entry.
 
Thanks in advance.
 
Steve