This is very simple beacuse i have created a couple lines of code that will do this for you
So set a variable as msg and then use this code. it popup in a VBS message box.
CODE:
@echo off
echo %msg% >vbs.txt
copy vbs.txt vbs.vbs
del vbs.txt
start vbs.vbs
timeout /t 1
del vbs.vbs
cls
This is just something i came up with it should work for most of your message needs and it also works with Spaces unlike some batch scripts