Does Dell’s OEM operating system works for Alienware as well?

If you have a copy of Dell's OEM version of Windows 7, there is no reason to believe that it will not work with your Alienware machine. When a OEM (Original Equipment Manufacturer) creates their own version of Windows disc, they do not change the original OS in a way such that it will only work on their PC. The OEM disc usually have customized wallpapers, themes and some other programs coming from the manufacturer, other than that it is just another copy of Windows. So there are absolutely no risk of losing anything if you install your OEM version of Windows on a Alienware machine. After installing the operating system, you also need to install the necessary device drivers for your hardware, like graphic card, sound card, LAN. While most of the hardware should automatically work as Windows contains the basic set of drivers for them to work, it is always advisable to install specific drivers from manufacture's website for distinct hardware in your PC. Also remember that there are no risk of screwing up one's hard disk because of a bad installation of operating system. At most the system won't boot up but that is no way going to affect your hard disk.