Do you have Poser 4? If you do, there is a men's t shirt in the characters/mens clothing menu. The texture template is on the Poser 4 Content CD. Check the free stuff for t shirt textures. That will help you figure out how to do the work. If you have Poser 3, You will have to put your t shirt pictures onto the body texture map. All this can be done in PhotoShop.