An AirPort Extreme card (when used in the correct computer) will allow the Mac to connect to 802.11B and 802.11G networks. Most wireless networks are based on the 802.11B or 802.11G standard, so that means the Mac can then connect to most wireless networks. Is that what you're after?
FWIW, not all Macs need or can even use the AirPort Extreme card available in the Apple Store. If you're after wireless access, tell us which Mac you have and we can tell you which card you need, if any. 🙂