No, the planet Nibiru is a myth. Supposedly it was a twelfth planet orbiting the sun that was discovered (or predicted) by the Sumerians. According to the prediction, this planet comes near the earth every few thousand years, and is scheduled to reappear in 2012 and cause a catastrophe on earth. This makes a good plot for a huge special effects extravaganza movie, but it has no basis in facts.
If you're interested in more detailed information on this, take a look at this page .
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them