The High Holy Days are always early or late, never on time.
In 2010, they will be especially early:
September 9/1 Tishrei, Erev Rosh Hashanah
September 17/9 Tishrei, Kol Nidre
September 18/10 Tishrei, Yom Kippur

There are many explanations for why the first of Tishrei is considered to be the start of the New Year. The Torah sets this day apart as "a memorial proclaimed with the blast of the Shofar". According to tradition, it is the anniversary of the creation of Adam, the birthday of the human race. At first, Jews used the exodus from Egypt as a starting point for numbering years. Later, the destruction of the Temple was considered the focal point. Finally, however, the sages went back over the biblical record in terms of personal life spans, equating the years mentioned in Genesis as equivalent to our own and the seven days of Creation as days like our own. This is how they arrived at the number we now use, 5770: Five thousand seven hundred and seven years since the Creation of the World. The Torah refers to the month of Nisan (when Passover occurs)as the first month of the year in the Jewish calendar. It is the Mishnah which first refers to Tishrei (the 7th month, according to the Bible)as the beginning of the year. Actually, there are four New Years in the Jewish calendar. The first of Nisan is the New Year for Kings, the date by which the Kings of Israel calculated their reign. The first of Tishrei (Rosh Hashana) is the New Year for Years, by which years were counted. The first of Elul is the New Year for animals and the 15th of Shevat (Tu B'Shevat) is the New Year for trees.

And you thought it was simple.