What about the story of the "Rich Man and Lazarus" indicates whether it is a parable or not? To extend this previous question, what about the text of the story of Lazarus and the Rich Man indicates whether it should be considered a parable or an "actual" account?
One thing that seems to distinguish parables from accounts of actual events is the absence of specific names for the people in the parables.  In the parables we read, "A sower" (Luke 8), "A rich man" (Luke 12, 15), "A man" (Luke 13, 14), "A Samaritan" (Luke 10).

However, in the account of the Rich Man and the Beggar, we are actually given the name of the beggar.  This is quite a distinction from all the other parables.  In addition, Jesus tells us that the rich man saw another specific man--the patriarch Abraham.  

So, the fact that the rich man's name is withheld does support the idea of this being a parable.  Yet, the fact that two other specific people are identified by name seems to be stronger evidence to support the idea that this was an actual historical event with actual people.

The significance of this story comes in the reference to someone rising from the dead, as Jesus states that even if someone rises from the dead, some will not believe.  This is fulfilled in the fact that Jesus rose from the dead, and even the chief priests of the day continued in their refusal to believe in Him.

For reference:


  19 “There was a rich man who was clothed in purple and fine linen and
  who feasted sumptuously every day. 20 And at his gate was laid a poor
  man named Lazarus, covered with sores, 21 who desired to be fed with
  what fell from the rich man's table. Moreover, even the dogs came and
  licked his sores. 22 The poor man died and was carried by the angels
  to Abraham's side.The rich man also died and was buried, 23 and in
  Hades, being in torment, he lifted up his eyes and saw Abraham far off
  and Lazarus at his side. 24 And he called out, ‘Father Abraham, have
  mercy on me, and send Lazarus to dip the end of his finger in water
  and cool my tongue, for I am in anguish in this flame.’ 25 But Abraham
  said, ‘Child, remember that you in your lifetime received your good
  things, and Lazarus in like manner bad things; but now he is comforted
  here, and you are in anguish. 26 And besides all this, between us and
  you a great chasm has been fixed, in order that those who would pass
  from here to you may not be able, and none may cross from there to
  us.’ 27 And he said, ‘Then I beg you, father, to send him to my
  father's house— 28 for I have five brothers—so that he may warn them,
  lest they also come into this place of torment.’ 29 But Abraham said,
  ‘They have Moses and the Prophets; let them hear them.’ 30 And he
  said, ‘No, father Abraham, but if someone goes to them from the dead,
  they will repent.’ 31 He said to him, ‘If they do not hear Moses and
  the Prophets, neither will they be convinced if someone should rise
  from the dead.’”  Luke 16:19-31 ESV