The entire Sunni-Shia thing is a little overdone. It seems that Americans have recently discovered that The Muslims aren't the Borg, and have various sects in Islam just like in Christianity, and now they're trying to explain everything in terms of Sunni vs. Shia (leaving out significant facts, like that the Shia in iraq fought against iran during the Iran-iraq war.)

But in fact Iran is not the biggest supporter of Hamas -- the Arabs are. Israel tries to pin it on Iran for propaganda reasons (in fact israel itself helped Hamas rise, as a way to undermine the PLO.)

Iran doesn't care if you're Sunni or Shia etc. Iran also backed the "terrorist" ANC and Mandela when the US and Israel were backing the Apartheid regime, and later Mandela came to iran and personally thanked them.