GameDebate offers system requirements for Tropico 3, the island dictator sequel that's currently in closed beta testing (thanks Mike Martinez). They say these are the recommended specs, and minimum stats are not provided:

Tropico 3 System Requirements*

Intel CPU - Core 2 Duo E6400 2.13GHz
Nvidia Graphics Card - Geforce 7600 GT 256MB
Direct X - 9
Ram - 1 Gbs
AMD CPU - Athlon 64 X2 Dual Core 4800+
ATI & Intel Graphics Card - Radeon X1600 Series
Hard Disk Space - 5 Gbs

* System requirements displayed are based on recommended system requirements and should be used as a guide only.