Christmas script help

Hi people,Christmas is coming    so i want to make a  script  that will display  some message like Merry christmas somewhere on Christmas day and for new year eve, also i wanted to  embed an image and put it as wallpaper on set time ie. to change the wallpaper when the time will change for the new year.
Any hints ho to do this.
Make an Autoit program that reads the wallpaper from a hardcoded location and sets it as a desktop background.Can i package the program and the wallaper in a self-extracting archive ?

Thanks in advance