Hello everybody and thanks for your answers!!!
Sorry for answring thislate.
Well, finally my troubles are gone, the drive got recognized and it's working now

What happened? Well...
After doing a lot of tests without success, I set the SCSI ID of the drive to unit 0, removed the termination jumper and put the jumper for the "force narrow" option, then I went to the SCSI menu of the blizzardppc and put the controller itself as unit 7 (the last one) and voilá, it worked!!!
So now the chain is termination (active with the controller if I understand correctly the blizzppc manual), then the HD as ID 0, a Plextor 40X cdrom as unit 1 and a Yamaha CDRW as unit 2 with the termination jumper ON.
Thanks again for all your useful answers.
So.. do you think this setup is donde correctly or should I remove the passive tertrmination jumper from the cdrw?
regards
Dragster