Question on Postmodernism, literature and communication

[naamagatus]

Tabouli and Pippin's recent posts have encouraged me to present this 
question, in the hope that people who, unlike me, have actually 
studied postmodernist literary criticism (e.g., Tabouli and Pippin) 
can clear this up for me. 

Well, here goes. From what I gather, postmodernism basically creates 
or upholds cultural relativism, right? Truth and beauty are regarded 
as specific to cultures or communities (forms of life or whatever). 
Now all this is meant to break the eurocentric, white, male, 
christian cultural dominance, right? Clear room for other voices to 
be heard - Vietnamese women? Bornean hunters? Yappese? etc.?
What I don't get is, if cultural relativism holds, how is it that a 
person from one culture can hear a person from another culture at 
all? If criteria of truth/beauty are cultural specific, then what are 
we left with other than cultural specific canons that are inherently 
incomprehensible and therefore worthless for other cultures?
In other words, how can true conversations be held between people and 
*particularly* between cultures according to the postmodernist view 
(that is, without accepting the humanist assumption of an underlying, 
common human nature?)

I'm not trying to be argumentative, by the way. It's just that 
postmodernism never manages to quite make sense to me.  

Perplexedly,

Naama