Building a compact WLAN Ethernet Port Adapter.

Hello,

Now I am programming my PLC trough a LAN connection, I want make it wireless.

I want to build a very compact WLAN Ethernet port (RJ45) Adapter. Like a Phoenix WLAN EPA:
http://eshop.phoenixcontact.com/phoenix/treeViewClick.do?UID=2692791&parentUID=&reloadFrame=true

Is it possible to build this with Arduino boards or shields? When yes: which boards or shields can I use?

Thanks