The HT4557 article you attached above says:
With Home Sharing in iOS 4.3 or later, you can stream your entire iTunes library over your home Wi-Fi network from your Mac or PC right to your iPhone, iPad, or iPod touch.
But if you tell us exactly what you're trying to do (e.g., play music from an iPad to a home WiFi system connected by AirPort Express), there may be a way (e.g., AirPlay, documented here: http://support.apple.com/kb/HT4437