Why wouldn't you want to play Online? The only real difference is that you can play multiplayer while being online, otherwise it is basically the same thing. --- Notch is god and Jeb is jesus One made everything and put the whole deal into motion and the other fixes everything and makes people happy~IHeartJessAlba
You could disconnect your computer for a minute, log in->offline and reconnect if you really want to, but you'll be stuck with the default skin. --- Proud to be EPic. I am uncreative and needed scaredofbears help to make a new sig
Note: This contains more information than requested... Just check the last 2 paragraphs for the relevant info.
To play the game offline, you need to download the client ( http://www.minecraft.net/download -- Windows only) & run that. It'll download all the game's core files onto the computer you play it on.
If the computer you want to play on doesn't have internet access, you have to take alternative methods... Pretty much grab a USB thumbdrive (recommended minimum size of 0.5 GB's) & install "Minecraft portable" on it.
See http://portableapps.com/node/30573 (current test version) or http://portableapps.com/node/25222 (Outdated version). This download only downloads the client & reroutes the data to your USB thumbdrive instead of the computer's HDD.
Just Run Minecraft Portable & login to download all the core game files.
On the computer you want to play one (w/o internet access), go to %appdata% (punch it in the start menu search bar... If you're on XP, go to Start -> Run. This will take you to a special spot in Windows ) & on your USB thumbdrive, go to USB:\PortableApps\MinecraftPortable\Data . Just copy the complete ".minecraft" folder into %appdata%
Just drop a copy of the client onto your desktop (or preferred location) & run it. You can leave the login prompt empty (as the computer won't reach it, being offline) when you hit login. You'll get an error that it can't connect to minecraft.net, so just hit "Play Offline" to launch the game.
It requires a bit of DIY work, but that's how you can play the game offline. Please be aware that when playing offline, you'll be using the default player skin (Steve) & will be known as "Player".
Hope this helps! --- ~TStodden Game Monkey likes you...