Any level cheat
Click on the single-player option. When the single-player menu appears type 'drdeath'. A Cavedog Entertainment bone will appear: click on it and you can play whatever level you like.

Build anything cheat
Select 'Construction' or 'Advanced Construction' unit and press Enter. When in the message mode just select the commander and press Enter again. You can now get yourself some meaty weaponry, such as the lovely Big Bertha or the Doomsday device.

Special cheats
Press Enter for the message box and then type in the following codes. We won't tell you what each one does, because that would spoil the fun, wouldn't it?

+AIMFROMPRIMARY
+AIMFROMSECONDARY
+AIMFROMTERTIARY
+ANTIALIAS
+ASSERT
+ASSIGN
+ATM	Gives 1000 metal and energy
+BECARRIED -
+BIGBROTHER -
+BURNALL -
+BURNONE -
+CDPLAY	Same as +CDSTART
+CDSTART	Start CD music
+CDSTOP	Stop CD music
+CLOCK	Show game clock
+CONTOUR #	Display a 3D contour; # is 1 to 15
+CONTROL # 	Control a different skirmish AI; # is 0 to 3
+DEBUGBREAK
+DPRINT
+DITHER	Dithering instead of line of sight
+DOUBLESHOT	All weapons do twice the damage
+DR
+DROP
+EDGE
+FEATURE
+FILM
+FILMSPEED
+FSHADOW
+GIVE
+HALFSHOT	All weapons do half the damage
+IFACE
+INCLUDE
+ILOSE	You lose
+IWIN	You win
+KILL	Kill every unit (including yours)
+LIGHT#	Darker structures; # is 1 to 1000
+LINE%D
+LOS	Same as +NOWISEE
+LOSTYPE
+MEM
+MEMDUMP
+MOVE
+MUSICMODE
+NETSTATS
+NOENERGY	Drop your energy to 0
+NOMETAL	Drop your metal to 0
+NOSHAKE	Stop explosion screen shakes
+NOTOKTOBUILD
+NOWISEE	Full map; disable line of sight
+NUMLINES
+NUMTABLES
+OKTOBUILD
+PROFILE 
+QUERYNANOPIECE 
+QUERYPRIMARY
+QUERYSECONDARY
+QUERYTERTIARY
+RADAR	100% radar coverage
+RCACHE
+RELOAD
+SCROLLSPEED
+SCREENCHAT
+SEALEVEL
+SEARCH
+SELBOXES
+SELECTABLE
+SHADOW	Toggle object shadowing
+SHOT
+SING	Units sing when given orders
+SOUND3D	Toggle 3D sound
+SWEETSPOT
+SWITCHALT	Switch between squads with # keys
+TABLE%D
+TABLEINFO
+TREEDEATH
+TSHADOW
+VIEW #	See a player's metal and energy; # is 0 to 3
+ZBUFFER