The Alienware Edition typically includes specific desktop gadgets (remember Windows Gadgets?) that monitor CPU performance, RAM usage, and network speed. These gadgets are skinned to look like holographic displays or alien interfaces, adding to the immersion.
The most immediate difference is the "Alienware Skin." This usually replaces the standard Windows Aero theme with a custom theme often called "Alienware Darkstar" or "AlienGUIse." Windows 7 Alienware 32 Bit Iso