This could prove to be a stupid question but I've been trying to figure this out for days..

I have an '08 is250 and I'm trying to figure out if its xm ready or if i need to buy an xm radio. If the car is xm ready which I think it is, how do i go about hooking it up?

 

yes its XM ready unless you have the receiver with the car and the dealer added it. You can get the kit from Sewell Lexus, in the vendor section, and there is a DIY install thread in the FAQ section for the ISx50. Its in the trunk and easy to do. You can pay the dealer to do it but I think its ~500$ to install it?