Luckily, I don't have a problem with my fingernails. But there has been alot of discussion here about this product:
If you do a search, you'll probably find more threads about it.
Knox, the gelatin folks, have a product called "Knox for Nails". I took it everyday for a year, because I picked up a fungus from gardening and wanted my toenails to grow out faster. I did notice a difference in my fingernails, but the store I was getting it from stopped carrying it!
I've looked in all the stores around here, like Riteaid and Walgreens...none of them have it!