You might be up against a couple of problems here.
1. If the car is not prewired for XM it won't really matter if you have the module... you won't really have a way to plug it in. I haven't looked at a non-XM equipped vehicle to see if they use a standardized harness or not, they might use one harness for U2K vehicles and one for vehicles without. (U2K is the factory RPO for XM radio)
2. Those parts are not available to your GM dealer. They are on what is called "parts restriction". We cannot order one, we have to call GM and "convince" them that we need one. Then they automatically ship one to us for warranty repairs.
3. You cannot install one that has been used in another vehicle. They are blanked out when they are shipped to us and as soon as we plug it in and turn it on, it learns the VIN of the car you just put it in. If you put it in another car it will be "locked". There is no way in the field to unlock one of these units that I know of.
The best way to add XM to a non U2K vehicle is by installing an XM direct kit. I am told depending on who manufactured the radio for your particular vehicle, there may or may not be an XM Direct kit available.
The only way to know if XM direct is an option is to remove the radio from the dash and get the part number off of it. I would then be able to call my radio supplier and check to see if it is available and get you a price.
You'd still need to install it.