PC World reports Windows 7 is less of a resource hog than Windows Vista. Here's a look at the minimum system requirements for the beta:
They call for a 1GHz processor (32- or 64-bit), 1GB of main memory, 16GB of available disk space, support for DX9 graphics with 128MB of memory (for the Aero interface), and a DVD-R/W drive.
Those are very similar to the recommended requirements for Windows Vista -- even though PC hardware will have advanced by as much as three years by the time the finished version of Windows 7 ships.
Microsoft noted that the Windows 7 requirements are for the beta version only and subject to change. But it has also said the beta is "feature complete," suggesting the requirements will not increase by much if the beta tests go smoothly.