Testing is a bit close to my heart, as I am a tester myself and have done Beta testing in that past.
Beta Testers as mentioned in previous post, is usually done by masses who volunteer for the games through on-line forums, they usually never get paid. Alpha testers are mainly employes of the company and they do get paid.
Now there are ways if becoming a tester, one way is to do the ISEB software testing qulification, which has multiple levels, Foundation, Intermediate and Advanced qulification. The intermediate level is divided into Test Manager or Test Analysis.
Its a hard road and dont be fooled by the common mistake most people and companies make, thinking testing is all about running test, or in gaming industry about playing the game. I have spend a week creating a character with different colour hair, different type of style, level it to level 1 and then delete it, and start from begining, all that to make sure the character creation is not bugged.
To be a tester you need to have a different mind set, I love it and would not change it for the world, you need to decide if its for you.