Like you, I have a huge .emacs that I've acquired over the years.  Here's 
what I use to comment out a C region with #if 0:

                (define-key c-mode-base-map "\C-ci" 'if0-region)

; function to comment a region using #if 0

(defun if0-region (p1 p2)
  (interactive "r")
  (let* ()
  (goto-char p1)
  (beginning-of-line)
 
  (insert "#if 0\n")
  (goto-char (+ p2 +9))
  (beginning-of-line)
  (insert "#endif\n")))



From:   Harry Putnam <reader@newsguy.com>
To:     help-gnu-emacs@gnu.org
Date:   12/02/2010 05:06 PM
Subject:        Wrap predefined text around region
Sent by:        help-gnu-emacs-bounces+kgold=watson.ibm.com@gnu.org



Can anyone show an example of how to do something like this:

I want to wrap this:

  # [HP 101202_15:55:07 
  # ] 

Around the selected text... 
   <selected text region here>
   <selected text region here>
   <selected text region here>
   <selected text region here>

that is, select some text and press a key
combo ... voila... its now surrounded by:
  # [HP 101202_15:55:07 

  # ] 

Over the yrs I've acquired a fairly lengthy .emacs mostly by theft
from more skilled people.  Coding something like that is clear out of
my skill set.

I use lots of `skeleton' things for inserting various predefined texts
but don't know how to make that happen to selected region.

Usually given an example, I've been able to hack it up to my needs.