In regards to the calender the Islamic calender is a purely lunar calender which means that by the Gregorian calender it falls back 10 or 11 days every year (ie if Ramadan 1st is the 18th of october one year then the next year it is the 10th of october). I like the way it moves around because it means that over my lifetime I can celebrate all the differant Islamic occasions at differant times of the year. A month is from the sighting of the cresent moon until the sighting of the next cresent moon. There is quite alot of dispute in the Muslim community about whether a month should always be based upon the actual sighting of the moon or upon predicted sighting. Lots of people prefer the predicted sighting because it allows things to be more structured; calenders can be printed a year in advance, venues can be booked months in advance, council permits are easier to obtain if you say we want to block the street of on this date instead of saying we want to block the street off on this date maybe if the moon is sighted. Whilst I prefer to follow moon sightings I'm fairly relaxed about following predicted dates.
The first year of the Hijri calender was 622 by the Gregorian calender. It was the year that Muhammad (pbuh) and his followers moved from Mecca to Medina. In Mecca they were a minority group and persecuted but in Medina they established the first Muslim community. The current Islamic year is 1428 AH.

With 2 calenders I can have 2 birthdays every year lol. I think that next year both my birthdays are within a day or 2 of each other.
DH gets 3 birthdays because he comes from Afghanistan where they have a Persian calender as well. The New Year is on the equinox.

SaraJane, re the 5 prayers, they are at set times every day but the times are based on the position of the sun and moon. So for example, the time for the noon prayer is sometime between when an object's shadow is almost non-existant until it's shadow reaches it own length.As well as the 5 obligitory prayers one usually makes a personal prayer at the end and there are also extra optional prayers.
Prayer is regarded as the second most important of the 5 pillars of Islam. In a Muslim communityy most of the day is ordered around prayer times and on Friday when the noon payer is performed usually the whole city just comes to a stand-still.