My girl Merlot was very lame with Navicular disease (she was xrayed positive) when I got her a year ago. Her hooves were terrible - very long in the heel.
Within 3 months of correct BAREFOOT trimming all lameness had gone. Now she sprints around the paddock - just floating - NO ISSUE with navicular at all and all this was achieved simply through the trimming.
Totally agree with those of you who recommend Pete Ramey, or Dr Bowker. There is a great article about navicular here Navicular Disease - Information about Navicular Disease
and also Pete Ramey's article here http://www.all-natural-horse-care.co.../navicular.pdf
I include some pics of (the pregnant) Merlot zooming around pain free...
Hope this helps