The mtl import/export plugin is free. The only cost is the time your modeler may charge to bring in the model and export it. Or you can always ask someone on the forums for help in converting the LWO file and its textures to a file that can be imported into Poser.

First of all, what textures are you trying to import? Are they all image maps (jpegs, TGAs, PNGs, etc?) or are they procedural textures? Procedurals are really problematic to export. There is a way to do it, but it involves "baking" the textures, which eats up a lot of render time on a complex model.
Second, is the model UV mapped at all? As deci6el explained above, UV mapping tacks down the texture map to the geometry. In essence, it assigns a U and V coordinate to each vertex or point in the mesh (adding to the X, Y, and Z) coordinates. If you have to do UV mapping from scratch in LW, then you're going to have to pay for the modeler's time in any event. As I've alluded to above, the UV mapping in LW is not as easy to use as it could be, especially when compared to a program like UVMapper Pro. Poser is highly dependent upon UV mapping for textures and you will save yourself a lot of grief by ensuring that the UV Mapping is done properly before you even try to import the mesh into Poser.

If you want, PM me some details on this through my Renderosity account and I can try to give you a hand with this over the weekend.

deci6el: I've found UVMapperPro to be a lot easier to use than LW's built-in tools. The key is the ability to avoid distortions in the UVs--for example, when mapping a box, LW will tend to stretch the box sides so as to fill up the UV texture space. Normally, not a problem, but if you have to have a logo on the box side, correcting for LW's UV distortion is a pain. UVMP also allows you to preview the UV projection as you adjust the mapping on the fly for optimal view with minimal distortion. As you can tell, I'm pretty big on this distortion thing. 

UVMP is used by a lot of Poser users to create the texture mapping for their objects, so I decided to invest in it. It was about $60 if I remember. So far, I've been pretty pleased with it, but I haven't spent as much time with it as some of the power users.