Mon Colonel,
You are quite correct about the date for Easter 2011. My apologies to you (and to Hotel Mode) for the careless error.
However, Passover (like all Jewish festivals) commences on the evening before, i.e. 18 April this year. The Hebrew date for the beginning of Passover is 14 days after the new moon that heralds the month of Nissan.
Passover is observed for seven days in Israel, but for eight days in the Diaspora (like several other Jewish religious holidays). The reason for this anomaly is that, in Biblical times, Jews living outside "the Holy Land" could not be sure of the exact Hebrew date, so the extra day's observance is an insurance policy, if you will.
Best wishes and Hag Sameach (happy festival) from a veteran and confirmed matzah addict!
NB: None of the above implies that I will eschew the consumption of Easter eggs!