How do I get MAC adresses used in the NW ?

[SYNass IT Ubuntu / Linux]

Hello Ubuntu NW experts and cracks
My wireless Modem-Router-AP, a LinkSYS WAG 354G, crashed yesterday and 
I had to re-setup completely from scratch !

Within the present NW we have some different units like PC, PS with 
some MAC addresses !!

How can I identify these MAC addresses on my machine's screen ?
I need these to set access restricting to our existing ones alone ! ;-)

One more problem with wireless units i.e. PC's:
They do have 2 MAC addresses: 
one for Ethernet / wired and 
another one for wireless !!

How can I differ these two's ??

TIA for your support, 
cheers svobi