Press ENTER during gameplay, then type in the cheat.

Cheat Codes                 Results
1-58 (Select number)        Hear Star Wars quote
darkside (1-8)              Destroy enemy 
forceboat                   Press "," for invisible naval ship (screen must be 
                            over water when enabled)
forcebuild                  Instant contruction/research 
forcecarbon                 1000 carbon 
forcefood                   1000 food 
forceexplore                Show complete map 
forcenova                   1000 Nova crystals 
forceore                    1000 ore 
forcesight                  No fog 
galctic upheaval            Unlocks Decimator 
imperial entanglements      Unlocks imperial stardestoyer 
scaryneighbor               Speed boat with increased fire power(screen must be 
                            over water when enabled)
simonsays                   Unlock killer Ewok 
skywalker                   Win current mission 
tantive IV                  unlocks blockad run
tarkin                      Destroy every enemy 
that's no moon              Unlocks deathstar 

Submitted by jedi_tha_axe and unknown