If you Alt+Tab away to some other application, the game screen may not be displayed correctly when you switch back. The game should work on any modern PC - and most ancient ones, too - but keep in mind that it expects to be running full-screen and exclusively. (Although it might still take a while, as the download is a chunky 1.6GB.) The only 'catch' is you'll need an Electronic Arts account and a copy of Origin to download it, but that doesn't involve much more than providing your email address, and everything else is handled more or less automatically. This isn't a trial or restricted version, it's the complete product. There are also various smaller 'scenarios', quick skirmishes which you can use to learn the game or if you've only a few minutes to spare. The two bundled campaigns - Red Alert and Yuri's Revenge - follow on from the first game, and pitch the Allies and the Soviet Union against each other in a range of missions from small and stealthy to fast-paced, full-scale multi-unit battles. Command & Conquer Red Alert 2 is a classic real-time strategy game, first released for Windows back in 2000.
