As of 23 September, Notch is no longer taking orders for the game. He has put it on hold while he solves some server issues. Should be back up soon.

www.minecraft.net/prepurchase.jsp

You will have to have made a account first though.

Here's the deal. You can play for free, by playing the Classic version on the site already given to you by the others. But by clicking Buy now, you'll be able to make an account and then be taken to Paypal. Some where at the top you'll need to change the language if you're not Swedish...I had to change it, I kinda freaked at first...though it may give you some stuff about euro's...you'll pay about $13.77. If you but it now while the game is still in Alpha, you will never have to pay for it again or any of the new content that is released...not even when the Game goes full on finished! Once you completed the paying process, go back to the site and click Download, down load the type you need, Windows, Mac...etc. To play online, you need to have the internet connected, then run the program and start playing, once you start, you can exit out of the internet and play on. THAT! Is everything you need to know! I'm pretty sure...