The max texture size option in Acadia's screenshot is a P6 render option not a script. Apparently Poser 7 was coded to use texture maps more efficiently and so no longer required the option to scale textures down in the render settings. The script grichter mentioned and Silke linked to is a min shading rate script (also available on all characters and props on the parameters palette and as a general setting in the render settings) which determines how detailed the texture can be rendered. The lower the min shading rate, the crisper the texture, although this can also lead to longer render times.