What is a veto?
Bush is vetoing a bill which is expanding children's health care. He's vetoing it for 2 reasons. One, he thinks Democrats are trying to gain successes to earn "political points" in Washington. Two, it's not the bill he wanted to see, he says "I'm vetoing it and send it back in this form with these rules or I won't sign it."
This is not the point of the veto. If Bush wants to make laws, go into congress. It's congress's job to make laws and vote on them and pass them, the veto is for the president to exercise some huge control as a check on congress when they've been completely backwards. Remember that, it's a check and balance, not a twist of an arm behind a back to force congress to act in a certain way.
http://www.cnn.com/2007/POLITICS/09/20/bush.newser/index.html