Put the ignore.c file in your /rom/src directory.

-- Makefile
Add ignore.o to the O_FILES section.

-- act_comm.c
Somewhere up towards the top, add the line:
  extern bool is_ignoring(CHAR_DATA *ch, CHAR_DATA *victim);

In the do_tell function, before the lines:
  act( "&rYou tell $N '$t'&x", ch, argument, victim, TO_CHAR );
  act_new("&r$n tells you '$t'&x",ch,argument,victim,TO_VICT,POS_DEAD);
  victim->reply       = ch;

Add:
  if (is_ignoring(victim, ch)) 
  {
    sprintf(buf, "%s is ignoring you.\n\r", victim->name);
    send_to_char(buf, ch);
    return;
  }

-- save.c
Before the line:
  /* write alias */

Add:
  for (pos = 0; pos < MAX_IGNORE; pos++)  
  {
    if (ch->pcdata->ignore[pos] == NULL)
    break;

    fprintf(fp, "Ignore %s~\n", ch->pcdata->ignore[pos]);
  }

Before the line:
  KEY( "Id",          ch->id,                 fread_number( fp ) );

Add:
  if (!str_cmp( word, "Ignore"))
  {
    if (count >= MAX_IGNORE)
    {
      fread_to_eol(fp);
      fMatch = TRUE;
      break;
    }

    ch->pcdata->ignore[count]        =      fread_string(fp);
    count++;
    fMatch = TRUE;
    break;
  }

-- interp.c
Before the line:
  { "inventory",      do_inventory,   POS_DEAD,        0,  LOG_NORMAL, 1 },

Add:
  { "ignore",         do_ignore,      POS_DEAD,        0,  LOG_NORMAL, 1 },

-- interp.h
Before the line:
  DECLARE_DO_FUN( do_imotd        );

Add:
  DECLARE_DO_FUN( do_ignore	  );

-- merc.h
Before the line:
  #define MAX_CLASS                   4

Add:
  #define MAX_IGNORE		      (Put whatever number you want)

Before the lines:
  char *              alias[MAX_ALIAS];
  char *              alias_sub[MAX_ALIAS];

Add:
  char *	      ignore[MAX_IGNORE];

Compile, and cross your fingers!
Any questions, e-mail them to ruiner@mail.org