you use the sims2 home crafter plus its
http://thesims2.ea.com/getcoolstuff/homecrafter.php you then go into that and look on the sims 2 website for a tutorial or contact one of the creators on here on how to use it
you basically create new content and then open a paint programme and then open that file and put your image on it then overwrite the original file... refresh in the home crafter plus and it should be there... set it to be a paint or wall paper then upload to game