seems we hear this a lot (people's fog lights burning out quite frequently - Elky and mklaro have had these problems).
I'm doing a search right now in here to see how common it is (especially for 98's)
so far I came upon this:
(read what brapple wrote)
http://www.contour.org/cgi-ubb/ultimatebb.cgi?ubb=get_topic&f=3&t=007624&p= this one talks about inadequate seals, water getting in and burning the bulbs out:
http://www.contour.org/cgi-ubb/ultimatebb.cgi?ubb=get_topic&f=3&t=006766&p=