I have got WAG54G V2 Firmware 1.01.15, when I enabled MAC filtering, for wireless card for the laptop it did not work (I can not access the internet)!!!
Sometimes a device may have multiple MAC addresses. To make sure I enter a MAC correctly I usually follow this procedure:
1. Select Allow all and connect with your device (laptop)
2. View list of connected MAC addresses
3. Copy an paste into restricted MAC address filter list
4. Select Restrict Access / Permit only