If you don't want to wait till the official 1.0 release of Minecraft, you can already download and play the RC2 (release candidate 2). Here's how to download the file and install it.

According to Minecraft creator 'Notch', the final version will only feature minor tweaks and fixes, and RC2 is fine for reviewing purposes. I've been playing it, and have found no problems so far.

For Windows 7 users:

1. Download the .jar file. Click this link, and save the file.

2. Click the Start button

3. Enter %appdata% in the search box.

4. Click and open the 'Roaming' folder.

5. Double click the Minecraft folder, then the 'bin' folder.

6. Now delete the 'minecraft' file. Don't worry!

7. Drag the file you just downloaded into the bin folder.

8. Start Minecraft as normal. It will update and you'll be playing the new version!

For Apple OS X users:

1. Download the .jar file. Click this link, and save the file.

2. Open Finder.

3. Type this into searchlight: /Library/Application Support/Minecraft/bin.

4. Delete the minecraft .jar file. Drag in the version you just downloaded.

5. Start Minecraft as usual and you'll be good to go!