I live in Drogheda and can verify the horse-with-a-man's-face story. I remember reading it in the local newspaper when I was about 10 (c.1983). As I recall it happened to an engaged couple. The report (scared the crap out of me!) told how the couple's car cut out on a dark country lane, after which the entity appeared on the dark road in front of them. It appeared to be an ordinary horse, but when it stomped its front legs up on the bonnet and thrust its face to the windscreen they saw, to their horror, its human head. It screamed in at them for a couple of minutes before disappearing. They drove to the local hospital where they were treated for nervous shock.
Legend has it that in penal times the priest in that area visited the local landlord to appeal for more lenient treatment of his parishoners. He rode on horseback and his dog accompanied. The story goes that the landlord ordered his men to seize the priest, and a struggle ensued during which the horse stamped it's hooves on a window sill and the dog left its paw print on a window pane of the landlord's house. Apparently they are still there to this day (its private property). Anyway, all three were beheaded and this is said to be the origin of the horse-man.
I've never heard of any other sighting of the horse-man other than the one mentioned above, and also never heard the legend of the beheaded priest until after the report was published.
I've since looked in vain in the local library for the newspaper report. Thanks Justin, for the original post containing the woman's name - I can investigate further now...