Sending a “pop up” Message to another computer on a network with Vista.

Ok. So I have found out that in Windows 2000 you can send another user on a computer by going into command prompt and using Netsend

(Netsend [username] “message”)

But I want to be able to do it on my home computers which I have one computer with Windows XP and two with Vista. Is there any way to send a message pop up thing like Netsend?

Thanks