Charlie Russel from Microsoft written article to discuss the hardware requirements of Windows Vista.
Processor: Any currently shipping mid-range and better processor from Intel or AMD will be a good for basic functionality in Windows Vista. Lower-end processors will work too, but they won't provide the optimal user experience for most users and especially not for high-end gaming or video editing.
Dual-core processors with 64-bit support will be excellent for Windows Vista, he writes.
Memory: To take advantage of Windows Vista's functionality 512MB RAM is recommended. More advanced users will need 1GB of memory or more.
Graphics: The graphics solution must support DirectX 9 and needs to have at least 64MB of graphics memory.
Storage: The typical Integrated Drive Electronics (IDE) hard disk has a speed of 7200 RPM and a 2 MB cache. By selecting a Serial Advanced Technology Attachment (SATA) drive with an 8 MB cache and Native Command Queuing (NCQ), you can give your system a boost in performance, especially if your typical workload involves running several different applications simultaneously. The HDD is mostly the slowest component in a PC and by replacing it with a faster one you can mostly get a considerable performance boost.
For maximum compatibility a DVD drive that handles both -RW and +RW formats is also recommended.
Networking: For a laptop 802.11 Wi-Fi is recommended and for home PCs 100Mbps Ethernet.