Oh, ok. That quote was his reaction to a “draft” and not the final report.
(Theoretically the report was transformed accordingly into something Powell could stomach before reading it to the world.)
Powell was under pressure to use shaky intelligence on Iraq: report

According to the report, the draft contained such questionable material that Powell lost his temper, throwing several pages in the air and declaring, “I’m not reading this. This is bullshit.”

Here is the full text of the entire article in case the link goes bad:
http://story.news.yahoo.com/news?tmpl=story&u=/afp/20030531/wl_mideast_afp/us_iraq_powell&cid=1514&ncid=1480
Powell was under pressure to use shaky intelligence on Iraq: report
Fri May 30, 8:42 PM ET
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WASHINGTON (AFP) – US Secretary of State Colin Powell (news – web sites) was under persistent pressure from the Pentagon (news – web sites) and White House to include questionable intelligence in his report on Iraq (news – web sites)’s weapons of mass destruction he delivered at the United Nations (news – web sites) last February, a US weekly reported.
US News and World Report magazine said the first draft of the speech was prepared for Powell by Vice President Richard Cheney’s chief of staff, Lewis “Scooter” Libby, in late January.
According to the report, the draft contained such questionable material that Powell lost his temper, throwing several pages in the air and declaring, “I’m not reading this. This is bullshit.”
Cheney’s aides wanted Powell to include in his presentation information that Iraq has purchased computer software that would allow it to plan an attack on the United States, an allegation that was not supported by the CIA (news – web sites), US News reported.
The White House also pressed Powell to include charges that the suspected leader of the September 11 hijackers, Mohammed Atta, had met in Prague with an Iraqi intelligence officer prior to the attacks, despite a refusal by US and European intelligence agencies to confirm the meeting, the magazine said.
The pressure forced Powell to appoint his own review team that met several times with Central Intelligence Agency (news – web sites) Director George Tenet and national security adviser Condoleezza Rice (news – web sites) to prepare the speech, in which the secretary of state accused Iraq of hiding tonnes of biological and chemical weapons.
US News also said that the Defense Intelligence Agency had issued a classified assessment of Iraq’s chemical weapons program last September, arguing that “there is no reliable information on whether Iraq is producing and stockpiling chemical weapons.”
However, Defense Secretary Donald Rumsfeld told Congress shortly after that that the Iraqi “regime has amassed large, clandestine stockpiles of chemical weapons, including VX, sarin, cyclosarin, and mustard gas,” according to the report.