The question of whether Vicks Vapo-Rub works on toenail fungus was the subject of a University of Michigan study about a decade ago. Their conclusion was positive; they isolated the specific ingredients that worked, and received U.S. Patent 6,361,785 (look it up to see the results of the research).
Also note that 90% of toenail fungus is caused by four dermatophytes that are the same culprits in athlete's foot and jock itch. (Therefore, to prevent re-infection, one must get the fungi everywhere - nails, feet, & crotch. Also change towels regularly, and don't dry your feet first, then transfer the fungus to another place.)
The formula (based on the research study, (which I've adapted for a more natural cure) is: 1 part Menthol oil
1 part Thymol oil
1 part Camphor oil
1 part Lemon Eucalyptus oil
1 part Tea Tree Oil
5 parts DMSO
5 parts Aloe Vera
5 parts Rubbing Alcohol
(the oils can be bought on e-bay, DMSO in a health store)
Apply twice a day to nails and feet. I've suffered from this vexing problem for 40 years, as did my mother and grandmother. It works.