XP Not Showing my slave drive in Device Manager or Disk Management

I just added a WD Caviar 80G HD as a slave to a WD Caviar 40G. BIOS shows it installed as a slave drive but XP doesn’t even reflect that it exists in device manager OR disk management. I even tried DISKPART and RESCAN, etc., but NOTHING. I’ve checked just about everything! Jumpers, cables, etc. and it’s all set up right. The only thing I can think of is that the 80G is an older 5200rpm model and my master is a newer 7200 but would that affect it? Any help would be GREATLY appreciated.