They set up a parallel intel shop, under UnderSecDef Feith, to interpret the intel in a way that supported their preferred policies. But they really believed that Saddam had WMD (everybody did; not everybody thought it was a good reason to invade), and they believed he posed a threat (which was preposterous, but they believed it). Powell certainly didn't lie at the UN - everyone thought they had anthrax. The only one who came close is Cheney, who talked about Saddam "reconstituting" his nuke program, when he knew there was no evidence of that. But you can make the case that he assumed Saddam was, so it was not a lie.
It was not lies that got us into Iraq; it was just piss-poor judgment, and flawed grand strategy.