Hi,
You can find a good Wifi connection, for a few € (10days : 10€, 20days : 15€, 30days : 20€) which works in all the center of Amsterdam, from the Centraal Station to the bridge after Leidseplein.
The web site is :
www.hotspotamsterdam.com
You can pay on the site, or you can buy some cards for your connextion, like the phone ones, in some place in Amsterdam, like the Cafe Three Sisters on Leidsplein 2.
Have a nice trip, bye.
Diab'