What Iran wanted in return was for the US to raise sanctions against Iran, and dismantle the People's Mujahadeen, or PMOI or MEK or MKO (it seems to have several names), which wants to start a revolution in Iran. They wrote to the USA offering this in April 2003. BBC Newsnight has a copy the letter - it was sent via the Swiss from "the highest authorities" in Iran. Instead, the PMOI continue to live at Camp Ashraf, where Saddam housed them, although the Iraqi government wants them out.
Video here (about 20 minutes):
http://news.bbc.co.uk/1/hi/programmes/newsnight/6272661.stm (Click on 'Newsnight Player', or 'Latest Programme'; it should be up for about 23 hours from this posting). The first 10 minutes or so are background about the PMOI (they're quite strange - they expected 100s of members to divorce, and some set themselves on fire to protest the arrest of their leader); the politics starts around 10 minutes into it.
It includes Colonel Lawrence Wilkerson, Powell's chief of staff, and now strong critic of Bush. He says the State Department wanted the MEK disbanded; the Pentagon and Vice President's office didn't. They said "we don't talk to evil", so refused to talk to Iran. He says they criticised the Swiss for even forwarding the offer to them.
Way to go, Cheney - just because you wanted someone to help attack Iran later, you turned down the chance for proper peaceful relations with Iran.