"On a related note, with the dissatisfaction among repubs in DC, if the US had a parliamentary system, would a non-confidence vote succeed? ie, would enough Rs vote against GW to make a majority with the Ds?
Not as long as there is a Republican majority in either house."

A note:
A minority of Dems in the Senate could shutdown the govt- they could stop all bills from passing by filibustering. Essentially if they had a serious issue which had public support, the Minority party has a lot power.

Further note:
As a sort of general rule for most of time the American public chooses not to have Executive and both Houses controlled by one party. If the Republicans maintain control of both Houses in '06, the Dems will have an advantage in the Presidential race in '08- but that would require that the Dems stop shooting themselves in the foot.