According to NASA, a vessel with humans on it would take roughly six months to travel to Mars and another six months to travel back from Mars. In addition, astronauts would have to stay 18-20 months on Mars before the planets re-align for a return trip. In all, the mission would take roughly 2 1/2 years.
Other groups have proposed detailed routes to Mars and put them online. Here are links to the plans hashed out by Mars Academy and thinkmars.
Of course the more difficult question is, "How much is it going to cost?" One estimate of the costs involved in sending humans to Mars came during the George H.W. Bush administration. The range was from $80 billion to $100 billion. More recent studies, however, narrowed that to between $20 billion and $40 billion.