National Defense Authorization Act for Fiscal Year 2008 H R 4986 which was just passed states:

Congress finds that Iran maintains a nuclear program in continued defiance of the international community while developing ballistic missiles of increasing sophistication and range that:
(1) pose a threat to--
(A) the forward-deployed forces of the United States;
(B) North Atlantic Treaty Organization (NATO) allies in Europe; and
(C) other allies and friendly foreign countries in the region; and
(2) eventually could pose a threat to the United States homeland.

...

Essentially, this calls for the establishment of the controversial missile defense shield, which is threatening to reignite the cold war and start a new arms race with Russia.

The findings of the Congress contradict the NIE released last month which concluded with “high confidence” that “in fall 2003, Tehran halted its nuclear weapons program” and that "Tehran had not restarted its nuclear weapons program as of mid-2007".

http://presscue.com/node/41856

I'm wondering what the bill means by "eventually could pose a threat to the US homeland." As in Iran would sell nuclear missiles to 3rd party groups that would attack the US or what?

Roll out the nukes.

I'm wondering what the bill means by "eventually could pose a threat to the US homeland." As in Iran would sell nuclear missiles to 3rd party groups that would attack the US or what?

That's certainly possible. Iran is still one of the world's leading sponsors of terrorism.