Once installed, drivers are not usually something that are visible. The system should "find" them when the device that needs them is attached to the machine.
So, what happens when you connect the XM-PCR to your Mac?
This device is no longer supported by XM, they pulled it over piracy concerns
More reading, about the drivers, here:
http://javaxm.sourceforge.net/faq.html

Hope it helps

P