WAPs (Wireless Access Points) can be set up to prevent connections from a network card whose MAC address is not pre-approved. You set up the list in the WAP.
DHCP is Dynamic Host Configuration Protocol - basically it auto-configures the IP address, netmask, default gateway and DNS servers for each client that connects to the DHCP server - in this case the WAP / Switch (technically it is the switch part that is acting as the DHCP server).
Both the client and the server have to be configured for DHCP - the former to request it, the latter to provide it. Otherwise the IP config has to be set manually.
Another possibility for the failure to see your wifi network could be that it is set to 802.11b only, while the clients are 802.11g only (or vice-versa).
SD