The Metal Gear Solid Online Beta is starting on April 21st this year, and will last for two weeks. If you want to participate, you will have to pre-order the game at a major retailer like EB Games, GameStop etc. By doing so, you will also get a little bonus DVD which contains a beta code.
The “Metal Gear Saga Vol. 2” DVD contains extensive original video content, which primarily focuses on the interconnected history of the “Snakes”: Big Boss (Naked Snake), Liquid Snake, Solidus Snake, and of course, Solid Snake. Additionally, the DVD contains a compilation of the MGS4 trailers to date and a special Prologue video to MGS4.
An insert in the “Metal Gear Saga Vol. 2” DVD case is your ticket to the Metal Gear Online Beta, containing the Unique Product Voucher Code (UPVC) and instructions on redeeming the UPVC to download the Beta client via the PlayStation Store when the download becomes available. The download of the MGO Beta will be available from April 17th 2008 to May 5th 2008 and the game play will be available from April 21st 2008 to May 5th 2008.
Source – PS Blog