[redhead]

You might be refering to this thread where you would parse by reference instead of making copies like your swap function does.
Which would alter your code to be:

#include <iostream>
#include <string>

namespace stacy
{
  //swap() swaps string1 and string2, then prints the new values.
  void swap(std::string &string1, std::string &string2)
  {
    std::string holder;
    holder = string1;
    string1 = string2;
    string2 = holder;
    std::cout << "String 1 is now '" << string1 
                  << "' and string 2 is '" << string2 << "'." 
                  << std::endl;
    }
}



int main()
{
  std::string one = "one";
  std::string two = "two";
  std::cout << "Befor swap: " << one << " " << two << std::endl;
  stacy::swap(one, two);
  std::cout << "After swap: " << one << " " << two << std::endl;
  std::cin.get();
}