Paul, normal map creation is a fairly straight forward process. I haven't used the PS/Nvidia plugin so I don't know. With Poser you want Tangent. Normal maps do work inside of Poser and have for quite a few years. Don't be discouraged, keep at it.

In regards to map seams yeah that's a bitch ain't it? That's why seams are usually hidden, inside of thighs, under arms, etc. If you want seamless maps then you are going to need more ammo than a PS/Nvidia plugin (3dCoat, Zbrush, etc)

Sorry I can't be of more help to you, best of luck.

Comitted to excellence through art.