Here's some info from the League of Women Voters about registering for the upcoming election:
You can register to vote at any time during the year, but the last day to register for the September 15, 2009 primary election is August 21, 2009; and the last day to register for the November 3, 2009
general election is October 9, 2009.
To vote you must be
a U. S. citizen, a resident of New York City for 30 days by Election
Day, 18 years of age by Election Day, and you must be registered.
You can register in
person, or mail your completed Registration Form. Your registration is
permanent unless you move, change your name, or have not voted for 5
years. You may register at your borough Board of Elections (or any
agency participating in the National Voter Registration Act) on any
business day throughout the year. Forms are available from your borough
Board of Elections (see addresses below), town and city hall, post
office, political parties, various state offices, and the League of
Women Voters. Click here to print a blank Registration Form. If you are registering for the first time you must provide a valid photo ID.