It's trying to mount the 'root' (/) and '/usr' from the network. Try typing:
bootlist -om service
The output will probably be 'ent'.
To change it to boot from a cdrom, type:
bootlist -m service cd0 # a specific cdrom
or
bootlist -m service cd # any cdrom device
Look at the manpages for the bootlist command for more options.
Also, you can pres F1 when the RS/6000 LOGO appears and go into SMS where you can select the correct device to boot from and configure the multiboot options. I find that pressing F1 multiple times or until just after the keyboard icon appears works best. Good Luck!