I think that I have tried /g already, but /g only enables xcopy to copy files to a destination which does not support encryption. This is not what I want, the external disk does support encryption and so the encrypted files are copied as encrypted. The problem is that it is a disk used for backup and if the computer crashed I would probably have problems recovering the encrypted files to another computer. Of course I can decrypt the files after copying, which is what I am doing now.
Of course I mean Windows7 transparent encryption.