mine is the Muro 100 - 512meg and it has a range of about 1 metre
which is all you need to get the sound onto your radio unless you have an external aerial. You might get another metre or so as my computer probably puts out a lot of rf mush.

the ads certainly make them look like you can use them on cars but I don't have a car radio. You have to have the earpiece plugged-in for Tx (as well as Rx).

They are illegal in the UK, which is why I had to get mine from the US and pay postage, import duty AND local taxes (at 17.5%).

Put Muro into yahoo and you get two re-sellers.