Getting an object out of Poser is easy, you just export it as an .obj or a .3ds file.
The tricky part would be to import a file into the game program.  Unless it
has an import option you'd have to hack the code.  Also unless the game
allows you to rig the character, you'd just end up with a static character,
you wouldn't be able to change its pose. Perhaps you need to ask this
same question on a games forum.