You could try a program called Screen Popup 3.00. We use it on our Windows 7 PCs, and it also works on Windows XP.
It looks nicer than net send - can be a little fiddly to setup, but once it's working it's a dream.
http://www.softpedia.com/get/Internet/Chat/LAN-Messaging-Clients/Screen-Popup.shtml
It's freeware so no cost.