I purchased an Arduino ethernet shield. I hooked it up to an ethernet cable of a laptop I don't use anymore, and figured out the IP and MAC adress. The MAC adress is "00 11 95 5A 9E 01"
So how did you figure this out? As far as I know (from reading the datasheet; I haven't actually gotten around to playing with my ethernet shield yet), the MAC address for the ethernet shield(s) are something that you have to provide from the arduino sketch, not something that is present on the board (as it would be on a PC NIC card.) All you really need to make sure of is that you don't use the same ethernet address as some other system on your local ethernet, and you don't accidentally use a multicast address (odd first byte.) It probably makes sense to use a "locally-administered" MAC address like "02 02 02 02 02 nn" (where nn is a number you pick.) (nice and distinctive, eh?)
What is that in ASCII? Just add 0x before it?
If you wanted to assign the MAC address "00 11 95 5A 9E 01" in a sketch, for setting up the ethernet shield, you would indeed use something likebyte macaddr[6] = {0x0, 0x11, 0x95, 0x5A, 0x9E, 0x91};