It seems undisputed that an Iraqi official visited Niger in 1999 to talk about trade. I think it's an inference, not supported by any direct evidence, that he might have been interested in uranium, because that's Niger's principal export. According to Talking Points Memo, a UK parliamentary committee investigated and stated that there were two sources for the report, only one of which depended on the forged papers:
http://www.talkingpointsmemo.com/archives/week_2004_07_11.php#003169TPM also says that, although British intelligence hadn't seen the forgeries, they'd seen a summary of the documents provided by Italy. Therefore, the Butler Report's attempt to break the link between the forgery and Bush's speech rests on pretty blatant weasel-wording -- stating something that's technically true (that U.K. intelligence hadn't seen the documents) but omitting another fact without which the first one is materially misleading. (That's the SEC's standard for truth in corporate communications to shareholders.)
All this is separate from the interesting question of who forged the documents. Regardless of who forged them (and who should perhaps end up sharing a cell with Karl Rove), it's probably more important to note that Bush made a major public claim based on documents that had been definitively determined by the U.S. government to be forgeries. It really seems like there was an effort to "launder" the fake information by sending it to the U.K. and then citing it as a British report, knowing that the British hadn't seen the underlying documents and therefore couldn't determine, as Wilson had, that they were forged.