The men were arrested in pre-dawn raids on December 3, 2004. They denied the charges during the trial, which began in June 2006.
Ansar al-Islam, which was formed in the Kurdish region of Iraq, is believed to have been behind attacks on US and allied troops in Iraq.
According to the indictment, Rashid also conducted monthly collections for the group in 2003-2004 and transferred the money to Iraq.
Judge Christine Rebsam-Bender described Rashid, 34, as "an important, leading member of Ansar al-Islam in Germany'' who had regular contact with the group's leadership in Iraq.
She said the 26-year-old Hussein was slated to succeed Rashid in that role.
The court found that Yousef, 33, had volunteered to carry out the attack on Allawi, and that he got approval by telephone from Rashid and Hussein.
Lawyers for the defendants have argued that, while they talked in hypothetical terms of an attack, they had no access to weapons or explosives and they had no realistic chance of carrying out any such plan.