Wireless networks will always present a different set of risks than traditional wired networks. The reason for this lies in the accessibility of their signals. Eavesdropping on a wired network requires physical access to a wire somewhere on the network, which means (at least) gaining access to a network jack somewhere within the building.
Wireless networks, on the other hand, make use of wireless access points and radios embedded in computers. The generated radio waves know no geographic boundaries. They travel through walls and windows and may be picked up by someone sitting in a parking lot. Short of shielding the building with lead, there's not much that can be done to prevent these emanations from leaving a company's buildings.
The best way an enterprise can protect itself against eavesdropping attacks on a wireless network is to use strong encryption. Implementing Wi-Fi Protected Access (WPA), or its successor, WPA2, will ensure that unauthorized individuals aren't able to intercept wireless network communications. That said, it's important to point out that WPA's predecessor, Wired Equivalent Privacy (WEP), is a badly broken security technology that offers little more protection than simply running your network in unencrypted fashion. For an illustration of this principle and more advice on building a secure wireless network, read my tip: Lessons learned from TJX: Best practices for enterprise wireless encryption.