i think that's what texture filtering fixes.  which is great if your on P7+, because you can apply it only to one material.  applied to a whole image, that'll slow things down.  i've had a similar problem with hair textures, and never found a solution. basically, the texture is so fine, it renders weirdly in Poser.  i have no idea if this is a problem in other renderers.  you can try rendering larger, getting your shading rate really low (and remember, the min shading rate is just a minimum, you actually have to select the group and change its shading rate), or maybe messing with the sampling and aliasing settings.  but i really don't know.