Usually if its not an open system (which it obviously isnt as they are asking for details of your PC) then its a MAC filtered system, meaning they only allow PC's to connect which are on their MAC list.
So yes, i would guess that they are asking for your ethernet cards MAC address. To find this out:
Click START
RUN
Type "cmd"
ENTER
Type "ipconfig /all"
ENTER
Wait a second and look down until you see something along the lines of "Physical Address" underneath the sub-title of your ethernet cards name. The address will look something along the lines of "0E-43-E2-00-A3-FD"
Also, as a side note - MAC addresses have nothing to do with Apple or Macintosh Computers, a MAC address is the physical address of a network hardware component and stands for "Media Access Control". A while back it had another name, called EHA, which stood for "Ethernet Hardware Address". That name makes a lot more sense to what you originally asked for
Hope that helps, dragon2309