FWIW, it seems to work the same in P4. I created some different textures with the same name and placed one in Poser 4, one in Runtime and one in Textures. I created a MAT file that simply referenced :Mytexture (don't remember whether I included the leading colon or not). Using this MAT, the texture that got loaded was the one in the Poser 4 folder, not runtime or textures.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken