The only way to test the content preview is to use actual device. There is no simulator or other tools available for testing. However, creating the content with the publishing toolkit should be straight forward and there shouldn't be any problems with it. "On-the-phone content preview" - Specification, available at http://www.forum.nokia.com/main/1,35452,1_41_3_1,00.html, specifies the content that can be packed to the .mm -file.
V / Forum Nokia