The obj format does not describe a real world scale, it just lists the co-ordinates by the sounds of it TG2 uses a scale that are 100 times greater than xfrog e.g. <0,1,0> in xfrog being a centimetre on the y-axis , TG2 using <0,1,0> as a metre.
Did you say yes for the xfrog compatability options ?
Is the source in cm option checked on the object importer ?