comment forcer le \n tous les x carracteres dans  
un textarea ?

avec ca je pense (msg poste par Sh@rdar ds topic la fonction qui vous simplifie le + la vie )
 
wordwrap --  Wraps a string to a given number of characters using a string break character.  
Description
string wordwrap ( string str [, int width [, string break [, int cut]]])
 
 
Returns a string with str wrapped at the column number specified by the (optional) width parameter. The line is broken using the (optional) break parameter.  
 
wordwrap() will automatically wrap at column 75 and break using '\n' (newline) if width or break are not given.  
 
If the cut is set to 1, the string is always wrapped at the specified width. So if you have a word that is larger than the given width, it is broken apart. (See second example).  
 
Note: The optional cut parameter was added in PHP 4.0.3