I think I was going the wrong route as hydra is not needed with rdesktop.
rdesktop can be used to brute force but I can't get it to work. Tried the following command.
rdesktop -u administrator -p passwords.txt 192.168.0.100
I understand that rdesktop needs patching but my version as installed on BT4-r2 is Version 1.6.0 which I think is the latest.
Any pointers would be helpfull
Many thanks not trying to bump my thread, just found out the info above.