[jQuery] $.getJSON

[jQuery] $.getJSON

hi,
i do not understand so well how the function getJSON works. i've read the documentation but i think i miss the point.
i would like to pass some argument/parameter to a php file which in return gives me som JSON answer.
therefore i wrote the following code:
$.getJSON("lg.php", 
{ start: 0, offset : 5 },
function(data)
{
 $.each(data, function(i,item)
 {
  alert(item[0].id + "\ni : "+i);
 });
});
1.how can i get each item without using a hardcoding 0 or 1 as index ?
i did not find anything into documentation :-(
thanks a lot for feedback
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Alain
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Windows XP x64 SP2 / Fedora 10 KDE 4.2
PostgreSQL 8.3.5 / MS SQL server 2005
Apache 2.2.10
PHP 5.2.6
C# 2005-2008