Which OSG methods are you using? Generally to convert a position/vector from Vizard to OSG reference frame you just need to negate the Z value. To convert a quaternion rotation from Vizard to OSG you need to negate the X and Y values.
OSG does use a Z-up convention, but you don't need to deal with that unless you are loading external models using the osgDB API. If this is the case, then you need to rotate the model 90 degrees about the x-axis by placing it under a osg::MatrixTransform with the following value:
Code:
osg::Matrix::rotate(osg::DegreesToRadians(90.0),osg::Vec3(-1.0f,0.0f,0.0f))