You...
Visa procedures completely dependent of your nationality. As far as I'm informed, western countries citizens should get a visa at Iranian embassy in charge for your natioanlity. Slovenian citizens can get Iranian visa for 38 EUR at Iranian embassy in Vienna. Israeli stamp in the passport will prevent you from entering the country.
... and your vehicle
Check whether your national green card includes IR (Slovenian does). Otherwise no available information from my part. No customs taxes, Carnet de Passages en Douane compulsory.
Diesel 165 IRR, petrol 1000 IRR (December 2007). Rumors have it petrol price is about to rise again, expected is a 60% increase in price. Diesel is freely available, except for the area NW of Tabriz where you are limited to certain ammount of litres. Iranians can only get 100 litres of petrol per month, limited by a vehicle-attached chip card. Foreigners have to find their own way to get it.