Ifyou dont wanna to show that you've used Joomla, you should delete the meta tags
meta name="generator" content="Joomla! 1.5 - Open Source Content Management"
It's quite simple
In Joomla 1.5.x you need remove just one line in this file:
Find this line and delete it (or comment it):
$strHtml .= $tab.'
p.s. its in 84 line usually...
Enjoy Hiding :) ...