In addition, the virtualized Windows XP Mode will require a PC with a Intel-VT or AMD-V enabled processor, minimum 2GB memory and 15GB of additional disk space.1 GHz processor (32- or 64-bit) 1 GB of RAM (32-bit); 2 GB of RAM (64-bit) 16 GB of available disk space (32-bit); 20 GB of available disk space (64-bit) DirectX 9 graphics device with WDDM 1.0 or higher driver
For comparison, here are the minimum specifications for Vista:
1 GHz processor (32- or 64-bit) 512 MB of RAM (for Home Basic); 1 GB of RAM for all other versions 15 GB of available disk space Support for DirectX 9 graphics and 32 MB of graphics memory (for Home Basic); 128 MB of graphics memory plus WDDM support for all other versions