First of all, you'll need to be at least 18 & have a High School diploma (or a GED) before you can even get your foot in the door.
Second, you'll want to search for a Quality Assurance (the technical name for a game tester) position... or even intern positions, if you want to get deeper into the industry. Ideally, check out http://www.gamejobs.com
here as most of the open industry positions are posted here. Otherwise, check company websites in the corporate area (it's usually a small link on the site, look hard for it).
Atari ( http://www.atari.com
) doesn't post job listings on their website, but Bungie ( http://www.bungie.net
) post job listings publicly on their front page.
Third, you'll most likely want to get yourself to California where the majority of game studios are located... or look at a company that you're interested & try moving there. Just be aware that most companies will only hire people who live nearby as they don't give anybody in the QA department a relocation allowance.
Fourth... Be prepared to have your life sucked from you! Quality Assurance can be a very demanding job! Expect to spend up to 80 hours a week at your desk, especially during "crunch time" (near release dates) where you may be practically living at your desk.
Finally, Don't expect a long-term career here... most entry-level QA testing may only be for 3 months. Unless you can impress your superiors, you may be out the door after that.
Hope that helps you out... although you'll more likely get depressed for the lack of QA positions at the moment. Just keep on searching periodically & you'll likely find something!
Best of Luck!