you need to make a copy of your .exe file (this is the file in your main directory that opens the game up for you. NOT the file that opens up the little "autoexecute" window that allows you to launch the game or update it and such)
So..you make a copy of that file.. then go into its properties and it will say something like
"E:\Program Files\Stardock\TotalGaming\GalCiv2\GalCiv2.exe"
What you want to do is put "cheat" at the end of that. it should end up looking like this
"E:\Program Files\Stardock\TotalGaming\GalCiv2\GalCiv2.exe" cheat
notice that I put the word cheat OUTSIDE of the quotations.
Launch the game using that icon.. and then when you are in the game you can hit Ctrl + a letter to activate certain cheats.
for more info on this, and possibly a better explaination.. you can go to the thread that I started a while back called "The C Word.. (cheats)"
Just use the search function to the left of this forum to find it.