System Requirements for Revit Architecture 2008:

Intel® Pentium® 4, 1.4 GHz, or equivalent AMD Athlon® processor
Microsoft® Windows Vista™ Enterprise, Business, Premium, or Ultimate; Windows® XP Professional, Home Edition, or Tablet PC Edition (SP1 or later); or Windows® 2000 (SP4)
1 GB RAM
3 GB free disk space
1280x1024 monitor and display adapter capable of 24-bit color
Internet connection for license registration
MS-Mouse compliant pointing device
Microsoft® Internet Explorer® 6.0 or later

System Recommendations for Revit Architecture 2008:

Intel Core® 2 Duo 2.40 GHz, or equivalent AMD Athlon processor
Windows XP Professional (SP2 or later)
4 GB RAM
5 GB free disk space
Dedicated video card with hardware support for OpenGL® spec 1.3 or later
Two-button mouse with scroll wheel