>I wonder if it is possible at all, but I am not a programmer.

1. I 6 months a go see a PATH for it.
2. Even Linux support changing of MAC adress form ifconfig.

>But while faking a
>MAC address may be useful for debugging, I think this i far too 
dangerous.

Btw. My goal to change my MAC adress is very simple:
My ISP give my internet connection only for my XYZ Network card.
I DONT wont to play with NAT, Masqurade etc...

And I have some 386 with no PCI slot so i cant use my "internet" 
ethernet card :( And changing the MAC adress in my old ISA ethernet 
card is propably only legal solution...