The US Government has been accused of meddling with Wikipedia entries.
According to an article in The Inquirer, a computer using an IP address attributed to the US House of Representatives was used to edit a Wikipedia entry on the invasion of Iraq. It was a Bush-friendly attempt to muddy the waters over the controversial question of whether Saddam had access to weapons of mass destruction, and to try to establish a link between the Iraq regime and al-Qaeda, according to the article.
This chimes with another piece on leaked-document site Wikileaks, in which the US military at Guantanamo Bay was accused of "deleting detainee ID numbers from Wikipedia last month, the systematic posting of unattributed "self praise" comments on news organization web sites in response to negative press, boosting pro-Guantanamo stories on the internet news site Digg and even modifying Fidel Castro's encyclopedia article to describe the Cuban president as "an admitted transexual" [sic]."
All I can say is that both sound feasible - the US government and military would want to control perceptions of its actions, especially when those actions are highly suspect. The whole WMD argument was laughable from the beginning, as were the supposed links the Iraqis had to al-Qaeda. Altering a Wikipedia entry for propaganda purposes would be fairly easy, as in theory anyone can edit the online encyclopaedia.