Are Facebook entries considered evidence that can be presented in court?

In addition to the answer given by the attorney from NY, I would like to point-out that there is a chance the relative may not deny writing/sending the messages.  The messages have legal significance, but it is possible the relative doesn't know the exact legal significance.  I can envision that a person would say in court, 'yes, your honor, I wrote those messages BUT....' in which case the statements are admissible. 

The law regarding the use of the internet and the rules of evidence is emerging every day.  E-mails, text messages, etc.  The general problem with the use of these things as evidence in a case is that it is not easy for the court to say for sure who wrote them on the other end of the communication.  Although I understand that Facebook requires a password to sign in, who is to say that the party that owes you the money did not give their password to someone else (or that they will claim that they did at the time of the trial on the matter) and that it was not them writing the entries?  Seek legal help with all of this.  A verbal contract to pay back a debt is enforceable and you may be able to show the court the entries but they may not be enough "proof" on their own. Good luck.