Yes you only pay for internet service and there are no sign up or monthly charges like for the Xbox Live
you sign up and it's free on a psp
When you sign up for the PlayStation Network, you can enter codes to get the game Pain for free.
You can sign up to the PlayStation Network by going into "PlayStation Network" on the XMB, then click 'Sign Up to PlayStation Network'. Or you can follow this link to sign up on your computer, then transferring your account to your PlayStation 3 console. http://www.us.playstation.com/PSN/SignUp
yes you just have to create a account (also you need a email address)
Get an Xbox.
The network is down more information is available at related question
It all depends on what you are downloading. There are some free stuff such as demos for games, themes and a couple of free songs for Rock Band.. :) But if you are planning on downloading games, then yes you will have to purchase them. Look at the bright side, the ps3 network is free!!
In order to connect to the Playstation store you must sign in to the Playstation Network and select the icon from the Xmb for the Playstation Store.
Yes it is
Live is an Xbox 360 term to describe there network and the PlayStation can not use it. The PlayStation online gaming is through the PlayStation Network (PSN) and to get an internet connection you need internet service and most likely a Wireless router. Once your PlayStation is connected to the internet the PSN is free and you can use the PlayStation store for free demos or to purchase games and movie downloads and add ons
PSN is free the cards are for DLC such as games or addons Live is the name if the Xbox internet service, Playstation is the PSN or Playstation Network and it does not have a charge to sign up. Network Cards are never needed except for purchases you want to make. Even then they are not needed, you can just use a credit card to put Money in your Playstation Wallet
You have to be 18