I'm not sure how many waypoints you are talking about, but I had (please see other post from today) a working Lowrance H20c and putting in waypoints by hand was simple and fairly fast. I do know that the file format needs to be .usr for the lowrance to recognize. I know this isn't much help, but I'm looking for freeware conversion apps also for you.
On a side note .. I'm a HUGE Steelers fan myself. Did you see the recently ex-steeler Joey Porter busted Levi Jones in the face out in Vegas over the weekend.