Thanks to Addict3d.org:
If you use VMware 4.5.x virtual machines, and need to run an image on multiple machines with software on it that requires them each to have a unique network card MAC address this tool will modify your settings files to create one at random on startup.
VMware MAC Changer will automatically modifie vmware 4.5.x settings files to insert random MAC addresses.
Run a vmware image on multiple machines at the same time that requires unique addresses.
Put it into the windows startup folder to create a new address every bootup, and add the path
to the image as the parameter.
example:
c:vmwareVMWare MAC Changer.exe "c:vmwareimageswindows98windows98.vmx"
To download the file, grab it
here.