O-edit is very easy to use, if you just have those .o-files like that Goalie_Mask.o-file. You just have to open it with O-Edit and go to Texture tab and then open the Manage Texture tab. Then you just load the mask graphics (has to be in bmp.format) and there you have your own 3D-mask.
You should also enable all the parts you can see on the top right corner.
If I'm not incorrect your "skin" looks now mirrored. Let's fix it. Go to the Options tab and from there to the Perspective View section. From it, select the Invert X and your temp is turned to the right way.
You can turn the mask around by grabbing the 3D-model with left-click and with right click grab you can move the mask nearer or further away.
Hopefully this info helped you!