The following post is from another post by L Mourits - A good explanation,
The command syntax is:
configure net [[location]:[filename]]
(from enable mode ofcourse)
Let´s say you want to load a config from tftp server with IP address 10.1.1.1 and file is named pix-conf the command would be:
configure net 10.1.1.1:pix-conf
you could also just enter "configure net" to start the wizard and answer the questions
Remember that the loaded config is merged into any existing configuration, so, best practice would be to first execute the "write erase" command and then the "configure net"
Hope this helps --