While I do have some other nifty programs, you don't need them to make a screen shot.
1) open up civ3. (or the civ editor)
2) get the screen centered on whatever it is you want a picture of.
3) hit the "print screen" button. This copies the current image on the screen to the clipboard.
4) open up ms-paint. This program comes with windows. (win95, at least. yes, I'm still running win95.) If you can't find a shortcut on your start menu, try looking in your windows directory, i.e.
c:\windows\mspaint.exe
c:\program files\accessories\mspaint.exe
5) once in paint, go to the menu bar and select 'edit', then 'paste'. or hit ctrl-v. same thing.
6) presto. instant screen shot. granted, it's a bitmap file, and it's huge, but even with ms-paint's limited capabilites, you can crop the image, add graphics, and add text.
see the attachment.