You want to map the caps lock key to control, not the other way around.
Emacs can be run either in a text console or in X (graphics mode); the instructions for remapping keys differs.
The text console uses a program called loadkeys and X uses xmodmap.
Some examples: http://www.faqs.org/docs/Linux-HOWTO...HOWTO.html#s15
Note that when using loadkeys, you will need to be root and also press ctrl+D at the end of the instructions. Or you can save the instructions to a file and run
cat file | loadkeys
Edit: Amani points out that you can use the KDE menus instead. Gnome, as far as I can tell, does not have this option, but if you use KDE then that
The menu may be simpler than editing the .xmodmap file.