The MAC address is already assigned to the wii and you can't change that. ( i guess you could, but can you say "void warranty")
If you add the Wii's MAC address to the wireless device you want you wii to connect too, it may aid in solving your problem.
adding your MAC address to your wireless device i guess acts as a trust between the wii and wireless stuff.
Also another thought, during your initial set up did your wii ask you if you wanted to set wireless up. if so did the wii detect any wireless points? If so did you select the wireless point you want to use?
just some thoughts. its late and i may have wondered WAY of topic i dont know