Windows 7 - User To User Messaging on a LAN Across Multiple Windows Platforms

On my Home LAN (SOHO) I want to send a message to a Specific user! Trouble is one is on Windows 7 Pro (W7P), Another on Windows 7 Home (W7H) and the other on Windows XP SP3 (XP3). All are Setup with the WorkGroup Name "HomeGroup".
XP3, has Messenger Service enabled and Started! On the W7P & W7H Machine's in the Task Manager I Cannot see the XP3 user Name???

The "Msg" command is fine between W7P & W7H, BUT NO GOOD for the XP3 Machine - On XP3 The "Net Send" command (and WinChat) fails. IN OTHER WORDS I CANNOT SEND OR RECEIVE A LAN TYPE MESSAGE TO OR FROM MY XP3 MACHINE.

See as I cannot see the XP3 User Name on either W7x Machines, I'm not surprised, and I've No Idea how I can acheive Multi-Platform Messaging without the Help of some rather expensive software (NETtalk XP).

Threads post here and other sites haven't help address the specific issue outlined above, so if anyone has a solution, would love to hear from You!!