.vimrc

function! s:replace(...) range "{{{
  if a:0 < 2
    return
  endif

  let range = a:firstline . ',' . a:lastline

  let tmp = @@
  silent exec range . 'yank'
  let text = @@
  let @@ = tmp

  let text =  substitute(text, '\C\V' . escape(a:1, '\'), escape(a:2, '&~\'), 'g')

  silent exec "normal! :". range . "change!\<CR>" . text . "."

endfunction "}}}
command! -nargs=+ -buffer -range Replace :<line1>,<line2>call s:replace(<f-args>)