If you arrive at Schiphol you can easily take the train to Utrecht. When you leave the arrivals hall, follow the signs to the train station. The trains in the direction of Utrecht leave from platforms 1, 2 or 3 and leave every 15 minutes. The trip takes about half an hour and costs about €8.
From Eindhoven Airport take the bus to Eindhoven train station, after which you can travel onward by train. The trip takes about 90 minutes and costs about €14, after which you'll be strolling on the Oudegracht within five minutes. Check www.9292ov.nl for timetables.
Adventurous travellers can also choose to fly to one of the German airports. The Cologne S-Bahn will take you to Cologne central train station, after which the ICE will take you straight to Utrecht. The hip Sky Train from Düsseldorf Airport will take you to the Düsseldorf Flughafen