Here's a quote from the CCP press release:
Looking good people!
CCP is releasing two versions of EVE Online: Trinity. Gameplay will remain the same in both versions and both will be available as free downloads. A Classic version of EVE Online: Trinity will be available December 5, 2007 for Microsoft Windows, Macintosh and Linux platforms at http://www.eve-online.com/download/. The Premium version of EVE Online: Trinity, which will include updated and enhanced graphics, will be available on Microsoft Windows on December 5, 2007 and to Mac and Linux subscribers in the first quarter of 2008.
The premium version is compatible with graphics cards capable of displaying Shader 3.0 graphics or better.