How to Launch Minecraft.jar

1. Open your browser to the site Open Jar Files. This site allows you to decompress JAR files right from the site, and then download them back to your computer. Click 'Choose file' to upload the Mincraft.jar file and 'Decompress' to open it.

2. Download and install the free program WinRAR. This program lets you open ZIP, RAR, JAR and other archive files. You can open these files after you've installed WinRAR by simply double-clicking on them. WinRAR can also create archives like RAR.

3. Download and install BitZipper. This program is free to try on a trial basis, after which you need to buy the full version to continue using it. The full version of Bitzipper costs $24.95 as of March 2011. The program lets you unzip archives like JAR, but it can also create file backups.