Without so much as a squeak Spore's system requirements have slowly matured enough from the primordial soup that they've posted themselves online.
Only the basic list is available at the moment and they cover Windows XP and Vista as well as the MAC system.
FOR WINDOWS XP
* 2.0 GHz P4 processor or equivalent
* 512 MB RAM
* A 128 MB Video Card, with support for Pixel Shader 2.0
* At least 6 GB of hard drive space
FOR WINDOWS VISTA
* 2.0 GHz P4 processor or equivalent
* 768 MB RAM
* A 128 MB Video Card, with support for Pixel Shader 2.0
* At least 6 GB of hard drive space
FOR MAC SYSTEMS
* Mac OS X 10.5.3 Leopard or higher
* Intel Core Duo Processor
* 1024 MB RAM
* ATI X1600 or NVidia 7300 GT with 128 MB of Video RAM, or Intel Integrated GMA X3100
* At least 4.7GB of hard drive space for installation, plus additional space for creations.*
* This game will not run on PowerPC (G3/G4/G5) based Mac systems (PowerMac).
For a more detailed break-down of what graphics cards are supported and some other additional notes then click here to visit the official Spore Spec list.
Source: Joystiq