One man is heard telling a another to clear out "forbidden material", and destroy the message afterwards.
But an Iraqi advisor, Amer al-Saadi, has said Powell's speech was a "typical American show complete with special effects".
Powell said the evidence proves Iraq is breaking UN's rules on weapons.
He said the US also has proof that:
He told the UN that Iraq also has programmes to make missiles which can fly more than 1,200 kilometres.
- Iraq has biological weapon factories on wheels that can be moved easily
- Saddam Hussein was trying to get materials needed to make nuclear bombs
- Iraqi scientists were threatened and told not to talk to the inspectors
- Iraq had lorries which were moving missiles at almost 30 sites - he had photos of these.
- Iraq is hiding senior members of Osama Bin Laden's al-Qaeda network.
Powell warned the UN they had to act now to stop Saddam Hussein - and not leave it for months or years.