To change your mac address at Leopard OSX there is a little ‘trick’ that is required. The regulair command with ifconfig does not do the job.
Start your terminal and run:
Airport

Enable airport but disconnect from network.
/System/Library/PrivateFrameworks/ Apple80211.framework/Versions/A/Resources/airport -z
sudo ifconfig en1 lladdr [new mac]

 
Ethernet

no Fix yet, if you know any let me know.