Regardless of the removal or the survival of the socialist party or Saddam, Muslims in general and the Iraqis in particular must brace themselves for jihad against this unjust campaign and acquire ammunition and weapons. This is a prescribed duty. God says: "[And let them pray with thee] taking all precautions and bearing arms: the unbelievers wish if ye were negligent of your arms and your baggage, to assault you in a single rush." Fighting in support of the non-Islamic banners is forbidden. Muslims' doctrine and banner should be clear in fighting for the sake of God. He who fights to raise the word of God will fight for God's sake. Under these circumstances, there will be no harm if the interests of Muslims converge with the interests of the socialists in the fight against the crusaders, despite our belief in the infidelity of socialists. The jurisdiction of the socialists and those rulers has fallen a long time ago. Socialists are infidels wherever they are, whether they are in Baghdad or Aden. The fighting, which is waging and which will be waged these days, is very much like the fighting of Muslims against the Byzantine in the past. And the convergence of interests is not detrimental. The Muslims' fighting against the Byzantine converged with the interests of the Persians. And this was not detrimental to the companions of the prophet.
"Convergence of interests" establishes the link, I think. Basically, Al Qaeda is stating that they can ally with other evils when their interests coincide, which they seem to think is the case in Iraq. Islamists such as Bin Laden see any government, socialist, communist, democracy, etc., as made up of infidels. That he refers to the socialists in Iraq as infidels does not mean he does not see an opportunity to ally when interests converge.