What could we do with a Half-Trillion dollars?

Hmm, after reading this article...
http://abcnews.go.com/WNT/IraqCoverage/story?id=1629118
I cant help but think that a Half-Trillion dollars could make this country pretty dang safe. Just think if we had spent it on homeland security, instead of a war, what we might have accomplished.
or...
What if we had spent it on education, cures for diseases, green technologies (like electric autos, renewable energy, etc), or a number of other things?
The US of A would be back to her old self, leading the world and setting the example,.. instead of breading hate, killing people and destroying nations, cultures, relationships, history, and whatever else that Half-Trillion dollars has funded.