I am concerned primarily with the SUNNI insurgency which the Iranians are definitely NOT helping because the foreign fighters among them hate Iran even more than they hate the U.S., because it is a Shi'ite state, and the locals among them, some at least, are showing a willingness to cooperate with the U.S. simply to curb the influence of the Iran-backed Shi'ite government.
That's not quite true - the Sunni insurgents have started using EFPs, and that technology entered Iraq via Iran. There may be direct help from Iran or there may be some filtering through from the Shia. Never underestimate the phrase "My enemy's enemy is my friend."
The Sunni insurgency is a VERY complex organisation made up of at least five distinct groups based on their ideological grounds, and dozens of smaller groups. So you can't really give a blanket answer to where the Sunnis get their training, or how much they get. But there is one thing in common - nearly all Iraqi men over the age of about 25 will have been in Saddam's army due to its conscription, and many men of middle age will have combat experience from the Iran-Iraq war. Add to this the fact that nearly every Iraqi family has traditionally had weapons at home, nearly every Iraqi will know how to operate an AK-47 at the very least.
Consider these groups, but remember that the lines between them blur:
1.
Secular Ba'athists - these are made up of Saddam loyalists. Most of them would have formal military training from being in Saddam's army, and anyone who joined them would have access to both large stockpiles of munitions and the knowledge of how to build IEDs from it. Ex-engineers for example.
2.
Secular Nationalists - these guys hated Saddam, but they hate the US almost as much if not more. They are patriotic Iraqis who are fighting for Iraq. These guys are NOT religious fanatics and aren't deliberately seeking martyrdom if they can avoid it. They will train and share knowledge within their organisations. Some of these groups have recently starting allying with the US to fight "Al Qaeda in Iraq." They also don't attack civilians, and have started attacking Al Qaeda in Iraq because of the carnage AQII is causing.
3.
Islamic militants - these are the ones fighting for Allah. There are varying degrees of fanaticism among them. Among the most fanatical are "Al Qaeda in Iraq" (which is NOT the same as Al Qaeda). These guys have trainers in their groups too, especially bomb-makers. It only takes a few people to know how to make a VBIED. They show others, who show others, and very quickly the knowledge is spread throughout the AQII cells. AQII is on the back foot now due to the recent Nationalist-US alliance.
4.
Foreign fighters - It seems only about 10% of the insurgents are foreign fighters (despite what the Bush administration claims) sometimes these guys hook up with the fanatics. When Fallujah was stormed by US troops in November 2004, there were a few foreign militias in the city. One of these seems to have been made up of Chechens - and those guys know how to fight. They trained as a guerilla army, they even had uniforms. They probably were another source of training for the Sunni groups in the city. They were pretty much wiped out during Second Fallujah.
5.
Mercenaries - these are the ones planting IEDs or attacking Coalition forces for money. And it tends to end badly for them because they don't know what they're doing and don't understand the American capabilities such as thermal imagers. But they're doing it mainly out of desperation. They probably don't have much training at all, be it formal or informal.
I read an article some years ago now that interviewed one of the insurgent snipers. He had never been trained as a sniper but discovered he had a natural gift for it, which he thanked Allah for. He was loosely in a cell, but mostly was on his own. It doesn't actually take that much training to be a sniper in an urban environment - the ranges tend to be very short and there are plenty of places to hide.
So to sum all that up, the Sunni insurgents have training from their time in Saddam's army and later training within their cells. These cells are very loosely connected but it doesn't take a lot of time to learn how to make an IED when you have someone to show you.
