There are a few different ways to find out about your past lives. 

The first is to explore them on your own through meditation.  There are a lot of guided meditations out there.  The standard practice seems to be having you imagine walking through a long tunnel or fog, then once you come out, looking at your feet to see what you are wearing.  You can probably find scripts for such meditations on the web or purchase guided meditations.  I know iTunes carries some past life guided meditations by Denise Linn. 

I have also used a series of exercises on the Past Life Exploration group on Yahoo Groups.  The strong point in that is that Rev. Mehitabel, the group owner, gets people to think about various aspects of their current lives to search for clues to their past.  Once you make a connection to one aspect of your past, that connection can be a spring board to help you remember more.  I've found Rev. Mehitabel's techniques to be very helpful in remembering my past.    For more tips on meditating in general, check out the Psychic Development page on the Eerie Canal website.

Denise Linn also has an excellent book out called Past Lives Present Miracles. It contains a long questionaire to help narrow down when and where you lived in past lives and what those lives were like. That may likewise help jog some memories of those past lives.

Then there are psychics.  This is the quickest way to get information on your past lives.  If you have any question as to whether a psychic is telling you the truth or just telling you a pretty story, pay attention to your gut reaction to it.  If what you are being told is true, it will feel right to you on some level.  Ask other people for recommendations to find a good one.  I can personally recommend Jessica Jewett.  There may be a bit of a wait before she can do a reading for you at this point in time.  However, she's good enough that the wait is worth it. I also do readings at Reincarnation Adventures

Another technique is regression by a hypnotherapist.  A friend of mine who is a hypnotherapist recommends this method only if you suspect that you have past life trauma issues affecting your current life that you want to resolve.  I did try a session with a hypnotherapist and have an article about it here. My hypnotherapist friend also wrote an article from his point of view. Brian Weiss has an interesting workshop on this that is available for audio download. It includes a hypnosis session that I found it helpful. However, it will not guide you as well into discovering things about your past life as working live with a hypnotherapist would.

Also, what should you expect when finding out about your past lives?  No matter which method you use, you probably aren't going to get a lot of names, dates, or other historically verifiable information.  The point in learning about your past lives is to help you incorporate the lessons you learned in them or still need to learn in your current life.  Knowing the details of who you were, where you lived, etc. can be a distraction from what the universe wants you to focus on in knowing your past life.  I personally remember 10 of my past lives and have no clue of what my name even was except for one of them.

When I do past life readings for people, I am usually shown scenes from their past life that are significant to what they need to know for the current life.  For one acquaintance, I was shown her drowning in a pond as a little girl, and was told by her after the reading that she had an intense fear of water.  For another, I was shown Henry III, which was an indicator of the time period, and then her as a navigator on a ship, who used the stars to guide her.  She is now a professional astrologer.  There is always a connection between what I see and their current life.

Good luck with your explorations, and I hope you learn something useful!