Source: Frontline Message Board
Related: Steam
Valve released the CS: Source FAQ the other day. Here is part of it.

How will Counter-Strike: Source be different from the Half-Life 1 based Counter-Strike?

CS: Source blends the intense teamplay of Counter-Strike with the advance technology of Valve’s Source engine.

What will the system requirements be for Counter-Strike: Source?

Min:
1.2 GHz Processor
256MB RAM
DirectX 7 graphics card
Windows 2000/XP/ME/98
Mouse
Keyboard
Preferred:
2.4 GHz ProcessorB 512MB RAM
DirectX 9 graphics card
Windows 2000/XP
Mouse
Keyboard