Armenia (Time to process: half an hour)
Enter the customs hall at its east side. Process your visa at the first cubicle on the left.
Then take your vehicle paperwork to any window which has somebody behind it!! This person will process your paperwork, checking your chassis number.
There is a US$20 customs surcharge payable.
You are then clear to leave. Take your vehicle through the gates at the west of the compound, and to the Russian border guard. Just for a laugh, hide your stock of cigarettes, and let them hunt. 15-love to me. Then go to the next set of Russian border guards on the bridge. 30-love to me in the cigarette game. I wouldn't mind, but I don't even smoke.
Iran (Time to process: half an hour, plus all of Friday!)
Park at the border hut on the bridge. Walk to the building in the middle of the compound and have your visa stamped.
Return to the vehicle, and take it to the first Portacabin - the same one listed in the Iran-Armenia crossing information section. Present the Carnet, and they do all the processing.
Then go to the next office down from the Portacabins - to the window at the left (west). Here, they issue you with a "Traffic Permit For Foreign Vehicles". It's a form which shows your allowed route through Iran, and has spaces for endorsements for any traffic violations.
You are waved on your way, with a smile.
There are no charges on the Iranian side.