Well, Islamic holidays are based on a lunar calendar so it isn't the same Gregorian calendar date every year (I believe it shifts by about 11 days each year if I remember correctly) -- so, the dates listed below are what it will happen to be this upcoming time..
(also note I'm far from an expert here

- so someone is free to correct me if they know better).
Ramadan - the 9th month of the Islamic/lunar calendar. It will start on about the 6th of November 2002 this year (that's later this week!). This is the month spent in fasting - obstain from food, drink, sex, and other pleasures from sunrise to sunset of each day. This is a holy month because it is the time during which Prophet Mohamed was revealed the text for the Q'uran. (Note, while it is holy, it is not a particularly festival or celebration).
Night of Power (has a specific name that I forget) falls on the 25th (I think) night of Ramadan (see above).
Eid al Fitre - the 1st day of the 10th Islamic month. it is the celebration to follow Ramadan. This year it will probably fall on the 4th of December.
Eid al Adha - 10th day of the 12th Islamic month. celebrates the anniversary of the mircale of when Prophet Abraham was going sacrifice his son, etc (story as is in the Bible). This tends to be the month that most Muslims try and go for their holy pilgramige to Mecca.
Birthday of Prophet Mohamed - has a particular name. I don't know when this usually falls as our family does celebrate it (some muslims do, though).
Death of Prophet Mohamed - has a particular name. I don't know when this usually falls as out family does not honor it thoughs ome muslims do (it's one of the shia vs. suni things - i believe). not a celebration but rather day of morning
i think that's about it though... not a religion very big on religious holidays so that really brings much more focus and celebration to the two Eids.