buy a new network card, that's the only way.....

There are cards out there that allow you to change the MAC address via
their builtin BIOS or their driver software. If you can't find the
option in one of these places, you are out of luck.

The MAC address is usually considered pretty static, because there are
allocated pools per manufacturer of network cards. Obviously they try to
avoid collisions of identical MAC addresses. So don't play around with
that address if you don't know what you're doing!

               Oliver Sturm

http://www.nthelp.com/NT6/change_mac_w2k.htm

under Linux you would just use:
ifconfig eth1 hw ether 00:FF:00:FF:00:FF

AFAIK after restart MAC address will be reset to previous value

       PZDR PSG

Don't worry.You do not need to buy another network adapter.

If you are using windows xp.Just follow the exactly step:
windows desktop-->My Computer-->right click to show the context
menu-->select properties-->select the Hardware tab-->Device Manage-->exapned
the net work adapter tree-->right click the network adapter you want to
change the mac adress and select properties-->click the adavanced
tab-->select Network Adress in the property list box-->there was a textbox
just bellow the text "value"-->check it and fill your new mac adress(No '-'
needed)

This will solve your problem under windows xp.And you should find a
application for the sample purpose under other windows os.And I am not quite
sure about the name of that application.

Regrads.
jianglinchun@diyinside.com