The definition of an artificial intelligence is a computer then can learn evolve and adapt to new situations like a human can. We can not really tell how close we are currently because technology is developing at faster and faster rates. For instance every year the average computers capabilities doubles. Technology is developing so fast that scientists and theorise that eventually we will reach a point that they call the "singularity" this point is where the advancement of technology becomes uncontrolled and technology evolves and advances by itself.
Scientists believe that an AI (short for Artificial Intelligence) will be made within the next either 20 or 100 years. However once again I want to point out that technology is constantly surprising humans with how fast it is advancing. For instance a few decades ago people believed that only humans could play chess yet we now have computers to beat the best chess players in the world. Also look at the flight to the moon. A mere 60 years before the moon landing people believed that man would never fly and a half a century later we were sending people into space. We have made surprising progress in the way of AI's and here is a quick overview of what we are doing and what has been done.
In order to create an AI we need to have a program that not only processes data and draws conclusions but something that changes by what data it absorbs. This would allow it to have beliefs philosophies be more self aware and also allow it to deal with other humans much more easily or maybe even other AI's. We have made very little progress in this field but we have been able to make the programs do some of these functions when in a controlled environment.
Also in order to create an aI we need to give it the ability to find patterns. We have made progress in this the greatest example is the computer chess masters. With these abilities the AI could help in medical situations and also more easily connect with humans.
An AI needs to be able to search through massive amounts of data to find the data that is relevant. This is called Data Mining. This is especially important in business to find information about how the customer reacts to various products. These types of programs are used in the various search engines you use on the web.
Then last but not least is actually physically building the brain that will house the massive amounts of software necessary for an AI. One of the better known projects in this field is called Blue Brain and it is a project that is being worked on in Switzerland they have made surprising amount of progress and they have even been able to map out large parts of the brain of a rat.