I have a callpilot 100 but the IP address is unknown I dont have a serial cable but I thought you could reboot the c/p in a certain stage and it would revert back to the default IP TIA
nope. you need a serial cable.
Believe there's only two ways, Do a reinstall or through the serial procedure.
If you know the hardware address (the MAC address), you can ping the IP range you suspect it to be in from a machine in the same subnet, and then check the ARP table.