98 mercury villager, clicking sound coming from front end.?

Hard to say. The only hint you give is braking. If its the axleshaft, the sound will be more prominant while turning. When you said while braking, it makes me think that it's more likely a brake problem. Remove your front tires and make sure you have nothing hanging or broken on your brake system. You'd be surprised what will cause brake and wheel noise. I can't count the number of customers I've had with front end noise that tuned out to be a rock stuck between the brake calipers and rotors.