If we don't have diplomatic relations with Iran, how do Iranians come to the US to study?

Factual Questions
1

Another Iran question.

I was looking through the IIE’s “Open Doors” publication about foreign students in the US, and I saw that Iran had several thousand students in the US. If we don’t have diplomatic relations with them, how do students come here? I’ve studied abroad in two countries, one of which does not have formal diplomatic relations with the US (Taiwan), and I know that visa procedures are at the very least stressful.

Also, how do US students get to Iran to study? The IIE numbers say that there were only 2 US students in Iran in 2007/2008 (down from 7 the year before).

Finally, I mentioned this to someone last night, and they said that SecState Rice had tried to make diplomatic relations with Iran more transparent but had gotten pushback from the administration. Is that true?

2

Wikipedia says the US are represented in Iran by an interest section in the Swiss embassy, and Iran in the US by an interest section in the Pakistani embassy.