Specs in sig...
AthlonXP 3000+ rig plays Far Cry @ 1280x1024 with "High" quality sound (5.1), "Very High" graphics settings across the board and medium AA.
Not really tested the maximum potential of my P4 rig, but I've run it briefly @ 1280x1024 with "Medium" quality sound (stereo), "Medium" graphics settings across the board except water (Very High) and shadows (High) - no AA - and that ran perfectly fine.
Shadows are a must for this game IMO - being able to spot enemies coming or hiding by the shadows they cast is just too cool