AFAIK -ALL- Western Digital drives support the security commands.
Are you guys booting from a DOS floppy disk w/o any loaded drivers,etc. including CD, Himem, etc.?
You MUST do so.
BTW: I've locked 5 WD1200DJ's (western digital 120 gig drives) w/o problems.
I also know that all of the WD1200's will lock.