The minimum hardware requirements to run Windows 7 have been made public - a 1GHz CPU, 1GM RAM, 16GB of free disk space and a DirectX 9c capable video card. For the first time in over a decade, the upcoming version of Windows will not demand more than the one preceding it.
For the 64-bit editions, it is recommended to have 2GB of RAM and 20GB of hard disk space.
Further, for the new Windows Virtual PC and Windows XP Mode, Microsoft recommends having 2GB of RAM, an additional 15GB of hard disk space, and a processor supporting Intel-VT or AMD-V (these standards for hardware virtualisation are supported by most Intel and AMD CPUs sold today).
Almost any netbook on the market today can run Windows 7 RC without much sweat. We even ran pre-release versions of Windows 7 on a desktop PC comprising of a Celeron 466MHz CPU, 512MB RAM, and 20GB hard disk.