Samhain is a night when the veil between our world and the spirit world becomes very thin, and it's a good time to do some divination! Samhain falls on October 31 every year in the Northern Hemisphere, so the date for Samhain 2010 is October 31, although in some traditions it may be celebrated on November 1. In the Southern Hemisphere, it is on May 1.
Unlike solstice and equinox celebrations, this date does not change from year to year in most NeoPagan traditions. However, it's important to note that in some branches of Paganism, sabbats are celebrated based upon the astronomical calendar rather than the specific date. If you're part of one of these traditions, your Samhain celebration may need to be adjusted a bit.