there is a program in KDE called KSnapshot.
also there is a command line tool called import. This is part of ImageMagick.
If ImageMagick is installed (usually it is by default)
The command :
will let you sellect with the mouse the part of the screen you want to capture.
If you don't want to use the mouse a command like:
import -window root screen.jpg
will capture the hole screen.See the man page for more info.