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A rez file sounds very much like a lithtech engine game. So most likely try winrez LT studio. Also considering it's a korean FPS, on lithtech I'm assuming it will also use the LTB format for models and DTX for textures.
The textures can be converted easily, just google for DTXconvert.

as to the models, you can try LTB2X to convert them to an X format. If that fails you will need another two tools. LTB to LTA by dirigien to convert them and modeledit (it's a lithtech tool) to open them and recompile them to LTB again. Though that might sadly strip them off the UVW data