@rooeytoo: You can purchase a radio with a car kit; a minor installation you can do yourself. (It takes longer to call customer service to activate the radio than it does to install it).The car kit consists of a bracket to hold your radio, an antennae and a power cable to plug into your cigarette lighter or power plug. The bracket is designed so that the radio is easily removed whenever you exit the car (plug & play).
Sirius radios work independently of the radio already installed. You can choose to hear Sirius audio through your existing radio or you can use a cassette adapter if you have a cassette player already installed.
You can also search the internet for vendors (ie. Amazon, ebay, Walmart, Crutchfield, etc.) selling Sirius radios; you’re not limited to buying from Sirius.