here u go !

u must put systems in same network as you know.

step1 : start --> run --> (type) services.msc --> (press) ok

step2 : find for 'messenger' services (you can press 'm' as well to find it)

step3 : double click it ! change status form disabled to automatic if it is 'disabled'.

step4 : press start button & finish the process.

step5 : open your command prompt

step6 : type the following "net send ComputerNameHere some messages overhere"

step7 : Enter to send happy