Impossible to find out anything about the service without an account.
Napster will never be getting my business until I can see what their "18 Million tracks" includes.
It is frankly ridiculous that the only way you can browse their catalogue is to sign up with a credit card. I don't expect to be able to play tracks for free; I'm quite comfortable with the subscription model, but the only way to entice me to stump up is to show me what music you have.
Spotify only has 15 million tracks because they've imported hundreds of cheap live albums, remixes and, worst of all, karaoke CDs. Sorry, Spotify, you are just insulting me. How can I tell Napster isn't just the same? At least Spotify allows you to browse, and even listen to, their catalogue before signing up.
Also, Napster claims to offer an MP3 store (http://www.napster.co.uk/product_info.html) but can anyone work out how to access it without signing up for a paid subscription?