Ash Wednesday is the first day of lent - a period of 40 days before Easter (not including Sundays). Easter is always on a Sunday, and therefore Ash Wednesday is always on a Wednesday. In 2009 Ash Wednesday is on Wednesday 25th February.
No. While Ash Wednesday is an important day to Catholics as the beginning of the season of Lent, it is not a Holy Day of Obligation. Ash Wednesday is however a special holy day and a day of abstinence and penance.