It's pretty clear that the war in Iraq was not really a war on terrorism, because the organization that fomented terrorist attacks on the United States (and later Spain, etc.) was not a national organization. The best we could do in trrying to dramatize our wrath was pursue the Taliban by supporting the Northern Alliance, and then declare that Iraq was a source of terror for whatever reason.
There are nine interesting reasons why we have not pursued terrorism using special operations (the only kind equipped to deal with that sort of guerilla organization on any real terms, I think) and they are discussed in an interesting and authoritative-sounding essay on the "showstoppers on this site. I found it very informative and pretty even handed, as well, avoiding partisan rants on either side.