One of my early arguments in support of Saddam Hussein's ongoing relationship with al Qaeda was that avowed al Qaeda terrorists were so quickly able to enter Iraq and get set up - not have neighbors ratting them out, be familiar enough with the area in which they stayed that they never made wrong turns and ended up in the middle of an American patrol, were able to hook up quickly with the Ba'athists so as to learn where weapons stockpiles were, etc.
Analogy: in high school (I was at a DoDDS school in the UK) I understood from friends that it was easy to get hashish - but I myself (scared to death of drugs) never saw a score being made; it was only easy to get if you knew to whom to go and where to talk to that person to avoid the MPs and other inconvenient adults intent on enforcing the law.
In short, I think al Qaeda had significant infrastructure in Iraq before the American invasion. I would dearly love to hear commentary on this, because it still seems true to me, intuitively.
As it relates to current "force strength" among guerrillas in Iraq, I've heard nothing to indicate that coalition forces or the interim Iraqi government has been able to lay hands on all the unsecured weaponry around the country. If there's a lot of materiel still out there, these conditions must be met for al-Zarqawi and his cohort to get it:
1. They must know where it is - that is, they must have in their ranks Ba'athists who had that knowledge before Saddam was deposed, and - a guess only - probably a good number of informed Ba'athists, not just a couple of them. Or, they must have written records telling where the stockpiles are. If the estimates of numbers of stockpiles I've heard bandied about are correct, it'd be impossible for a normal person to commit all their locations to memory. Ba'athists are undoubtedly in the ranks of the Z-man. But how many informed ones are left? (Of course, if I were al-Zarqawi, I would have picked the brains of any Ba'athist officers who came my way as my first act. This would constitute written records.) (Side note, added: one way for the guerrillas to acquire stockpile locations would have been from the horse's mouth, so to speak. See Belmont Club, Feb. 1 entry, as well as http://www.suntimes.com/output/steyn/cst-edt-steyn30.html for brief but suggestive comments on what Saddam might have been doing in the six months between Sept. 2002 and the start of the war.)
2. They must be able to get out of where they are.
3. They must be able to get to the stockpiles, with trucks. (Also added: I say "with trucks" because while an individual could probably move a backpack's worth of ammo or explosive, it seems likely that the guerrillas would want to limit their exposure risk by making as few trips as possible. A truck or van, minimum, per trip - my guess.)
4. They must be able to return to where they hide, undetected. (Also added: an email from an Army guy I know in Baghdad indicates that while they may think they're undetected, increasingly they aren't. Loose lips still sink ships, so my correspondent gives me no more details, but check out all the al-Zarqawi operatives who have been captured lately and see if you make the same inference I do: it's getting harder and harder to hide in plain sight.)
5. They must have enough room in their safe areas to store what they've collected.
Strategy/tactical buffs, enlighten me: is there any public reporting about weapons stockpiles?