Actually, I think the biggest change will come with the way a President McCain would handle the situation in North Korea. By far a more important issue than George's takedown of Iraq, the situation in North Korea has been shoved into the background by the younger Bush's administration. No matter what he did, McCain would do more about North Korea than George.
There was no reason for the immediate takedown of Iraq and, thus, nothing would happen except for a few grumblings in Washington about Hussein. The war, however, was most likely inevitable in the long run (we weren't about to let either Uday or Qusay seize power following Saddam's death, they were more insane than the old man himself). However, the war would almost certainly not be over oil, revenge, or money for friends (as these were the most probable unstated reasons for the war in OTL). It would not be over WMD's as Iraq most likely did not have any, as we have needlessly wasted the lives of 500+ American soldiers, plus scores of British, Italian, Australian, and Spanish troops and diplomats, to find out. Nor would it have been over Al Qaeda, as the former Iraqi leader was found to have no connections with the terrorist group. It, instead, would probably have been over something more mundane, like the justified reasons for the US bombing of Iraq in 1998 or the First Gulf War. It also may have come at the time of Husseins death, most likely anywhere from 5 to 15 years. No, I don't think the Second Gulf War, which would have gained the support of the UN, would have occurred until AT LEAST 2005.
However, we may very well have been in a war in Asia, or participating in a blockade of North Korea, as we cannot, and are at the moment, ignoring the nuclear weapons under development in the communist nation. We may very well have seen a Second Korean War by this time. With international cooperation, a war in Korea may look like a modern version of the First Korean War in the 1950s.