_CPU:
P4 1,6 GHz / XP 1600+
P4 2.0 GHz / XP 2200+
P4 3.0 GHz / A64 3000+
DualCore CPUs are supported. A 3500+ is fine.
RAM:
512 MB
1 GB
1.5 GB
recommended: 2 GB. reportedly 3 GB still makes a difference though.
Graphics card:
shader model 1.4 -> GeForce 5, most Radeons since 9000
GeForce 6600 / Radeon 9700 class
clearly faster than that
Recommended: At least a mainstream shader model 3 card.
Priorities:
1. A lot of RAM. More RAM = faster loading times.
2. At least a 3 GHz (or equivalent) CPU. More doesn´t hurt though.
3. A modern graphics card.