Thanks for your answer - I'm assuming the device you are linking to is the "Actiontec Ethernet to Coax Adapter Kit for Homes with Cable TV Service (ECB2500CK01)".
All the reviews for this adaptor are great - I'm just a little in the dark as to how I would use it for my application.
For starters, does the modem have to be in the circuit somewhere? The coaxial cable coming from the house to my workshop does not go through the modem or the wireless router (it is split off from the service as soon as it comes into the house).
Also, will I need two of them, or only one? I'm not seeing how they would have to be set up to work for me.