Easter, like Christmas (Feast of Saturnia--the week long Roman holiday celebrating the year's harvest) has pagan roots.
You'd be surprised at how the early Catholic church superimposed a lot of old Roman traditions into the Christian faith. When Catholicism became the official faith under Constantine, they sought to convert the bulk of the population by allowing them to maintain certain aspects of Rome's cultural heritage. The old holiday's and celebrations simply received Christian overtones. I suppose it's the thought of celebrating Christ's birth and death that counts the most, but still...
I don't know what this Zombie Jesus Day is. He did rise from the dead, but he most certainly wasn't a zombie. My suspicion is that someone has been watching too many horror films!!
