Spawning autonomous shell commands

[Hilary]

This may be partly a windoze question. I use this on a windoze box:

(defun espeak-region ()
  "Send the region to espeak"
  (interactive)
  (shell-command-on-region (region-beginning) (region-end) "espeak -v 
mb-en1 -p 50 -s 150 --stdin ")
  )

It works, but it locks up emacs until espeak has finished reading the 
text. Is there a way of spawning espeak as an autonomous process which 
can finish in its own time?

--
Hilary S