Interested in continuing Chell's puzzling teleportation adventure in Portal 2 ? Then this bit of news is for you: Valve has released the Portal 2 single-player demo, and it's available for download now at our sister site, FilePlanet.As long as you have 975.7GB to spare, you can see the full intro and prologue to the game Valve is calling its best ever, as well as four test chambers to work your way through.Follow this link to FilePlanet and you're good to go. And here's a bit of advice: the Portal gun can be obtained by moving to the first chamber and dropping onto a platform to your right.Portal 2 is being developed for Windows PCs, Mac OS, Xbox 360 and PlayStation 3. The game is set to ship on April 19.Can't talk, downloading.