From the Diablo III Open Beta FAQ:
- Log in or create a Battle.net account at http://www.battle.net
- Create your BattleTag™, which is required to play Diablo III
- Download the game client, install, and play between 12:01 p.m. PDT April 20 and 10:00 a.m. PDT April 23
Due to regional differences and features of the stress test client, Korean players will not be able to partake in the stress test weekend. However, beginning the week of April 23, we will be conducting a separate, invitation-only closed beta test that will give players in Korea a chance to try out the game, along with players in the regions of Taiwan, Hong Kong, and Macau.
What platforms and languages do you support?
For the stress test we're offering the client in English, French, and German for both Windows and Mac. At release the game will be fully localized into English, Latin American Spanish, Brazilian Portuguese, French, German, European Spanish, Italian, Polish, Korean, and Traditional Chinese for Windows, and English, French, and German for Mac.
This ladder reset, like all those before it, creates a clean slate where all ladder characters begin at level 1 with no previous items to help them. To participate, simply wait until the Diablo II realms return to service on May 2, log in to Battle.net, and tick the “Ladder Character” checkbox when creating a new character. You can track ladder character leveling progress by clicking on the Ladder button from the main Diablo II in-game Battle.net interface.