please please PLEASE format your code so that it's easy to read!
  (e.g. http://p2p.wrox.com/topic.asp?TOPIC_ID=11967)

Many editors will do it for you! Here's your code, reformatted. Any comments I have will be in the next post.

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
struct queueNode
{
   char data;
   struct queueNode *nextPtr;
};
typedef struct queueNode QueueNode;
typedef QueueNode *QueueNodePtr;
void printQueue( QueueNodePtr );
int isEmpty( QueueNodePtr );
char dequeue( QueueNodePtr *, QueueNodePtr * );
void enqueue( QueueNodePtr *, QueueNodePtr *, char );
void instructions( void );
int main()
{
   QueueNodePtr headPtr = NULL, tailPtr = NULL;
   int choice;
   char item;
   instructions();
   printf( "? " );
   scanf( "%d", &choice );
   while ( choice != 3 )
   {
      switch( choice )
      {
      case 1:
         printf( "Introduzca un Caracter: " );
         scanf( "\n%c", &item );
         enqueue( &headPtr, &tailPtr, item );
         printQueue( headPtr );
         break;
      case 2:
         if ( !isEmpty( headPtr ) )
         {
            item = dequeue( &headPtr, &tailPtr );
            printf( "%c a Sido Eliminado.\n", item );
         }
         printQueue( headPtr );
         break;
      default:
         printf( "Opcion Invalida.\n\n" );
         instructions();
         break;
      }
      printf( "? " );
      scanf( "%d", &choice );
   }
   printf( "Fin de Corrida.\n" );
   return 0;
}
void instructions( void )
{
   printf ( "Introduzca su Opcion:\n"
      " 1 Para Insertar un Elemento a la Cola\n"
      " 2 Para Eliminar un Elemento de la Cola\n"
      " 3 Para Salir\n" );
}
void enqueue( QueueNodePtr *headPtr, QueueNodePtr *tailPtr, char value )
{
   QueueNodePtr newPtr;
   newPtr = new QueueNode;
   if ( newPtr != NULL )
   {
      newPtr->data = value;
      newPtr->nextPtr = NULL;
      if ( isEmpty( *headPtr ) )
         *headPtr = newPtr;
      else
         ( *tailPtr )->nextPtr = newPtr;
      *tailPtr = newPtr;
   }
   else
      printf( "%c No Insertado. No Memoria Disponible.\n", value );
}
char dequeue( QueueNodePtr *headPtr, QueueNodePtr *tailPtr )
{
   char value;
   QueueNodePtr tempPtr;
   value = ( *tailPtr )->data;
   tempPtr = *headPtr;
   *headPtr = ( *tailPtr )->nextPtr;
   if ( *headPtr == NULL )
      *tailPtr = NULL;
   free( tempPtr );
   return value;
}
int isEmpty( QueueNodePtr headPtr )
{
   return headPtr == NULL;
}
void printQueue( QueueNodePtr currentPtr )
{
   if ( currentPtr == NULL )
      printf( "La Cola esta Vacia.\n\n" );
   else
   {
      printf( "La Cola Es:\n" );
      while ( currentPtr != NULL )
      {
         printf( "%c --> ", currentPtr->data );
         currentPtr = currentPtr->nextPtr;
      }
      printf( "NULL\n\n" );
   }
}


Take care,

Nik
http://www.bigaction.org/