For the full September 7 release of Spore itself, the requirements are mostly the same with the exception of hard drive space. Windows XP requirements are as follows:

• 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 the requirements are

• 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

System requirements for the Macintosh version of the game are:

• 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

You can go to the Spore web site for more specific info on what will be required to run the game. You can also take a look at the Sporepedia which is a place where people can upload their own creature creations and share them with others. You can even view them in the Creature Creator when it is released.