Tourist visas myabe work visas for Iran

Hi,
I'm considering in taking the plunge and visiting Iran in 2015 for a couple of weeks, but on a fauna nature tour. I understand that independent travellers from most western countries cannot even get a tourist visa, unless accompanied by a local guide/s. I understand ecotours do nature/wildlife tours in Iran, though a visit to either Eshafan or Persopilis would be a must too. There are even crocodiles in Iran, the marsh crocodile but only a few are left and they are found in the far south east of the country. Asian leopards are found in Iran too. It seems to have some beautiful landscapes like deserts, steppes, mountains and forests and an ideal climate too, not hot and moggy like Dubai. But I've heard the hospitatlity in Iran is legendary and the lovely pomegranate lamb and rice grub too. I do hope the west and Iran rekindle their relationships soon. Iran is supposed to have the best healthcare in the middle east as well. What's it like for westerners to get work visas for Iran? Maybe to help out in conservation national parks, engineering or I.T.  Can you get a cold drink in Iran like salt lassi or non alcoholic beer? Do western women need to wear a head dress all the time, even as a tourist? If so we need to respect that.