Try running the AC with heat on defrost. The AC will dry the air and eliminate the fogging. If this does not work check the plenum intake vents between the hood and windshield for snow, ice, wet leaves or other obstructions. Also make sure the cabin air filters are not clogged.
Do you know if you've done the AC Defroster mod listed in the FAQ/How To's section? If so, then you'll see the AC light come on when you switch to the defrost mode. That'll let you know it's working.
Another thing you may want to try is to get some anti-fog wipes from armor all. I use them in the spring and fall (our most moisture laden times) they work pretty well, mos auto parts stores carry them.