VMWare workstation will automatically generate MAC addresses for your virtual machines to keep them from colliding. If you need to set it manually you must change a few lines in the .vmx configuration file. change: ethernet[number].addressType to “static”change: ethernet[number].generatedAddress to: ethernet[number].address and set your address. delete any other ethernet[number].generated* for more information: http://www.vmware.com/support/esx21/doc/esx21admin_MACaddress.html