I'm sure you can find more information out xm radio at their website -
http://www.xmradio.com/index.jsp
There is information about how it works, what programming they have, and how much it costs.
I have Sirius Satellite radio in my Chevy Avalanche and love it so much, we are going to get on for the Ody.
So far we have seen an Alpine unit that we like. The only thing is that it is XM Satellite ready and not Sirius. However, it is still satellite radio and I'm sure the programming and stations they offer will be similiar. Same goes with their pricing.
Is is worth it? For us it is. In Sacramento there arent' any stations we like. For the Satellite radio, like our Sirius, we never hear the same some twice in the same hour or two and there are no commericals. We can listen to the news if we want to, there is even kids programs. So, for us, yes it's worth it.