One of the primary advantages that SCSI has over IDE is the ability to have more than 2 devices per channel and the ability to have more than one device active on the channel at once
http://www.xlr8yourmac.com/RAID/8600/index.html
includes tip for easy transfer of data from the old drive to the new drive
http://www.xlr8yourmac.com/G3-ZONE/IDE/
Plextor OS X/OS 9 flashers for PX716/712/708 DVD Burners
http://www.xlr8yourmac.com/IDE/plextor_ide_flasher.html
tips on installing two drives inside
http://www.xlr8yourmac.com/guest_rev1/
to B&W G3 rev 2 - Quicksilver G4 Towers
http://www.xlr8yourmac.com/IDE/add_2nd_drive/index.html
PB Expansion Bay Hard Drive Kit
http://www.xlr8yourmac.com/PB_G3/ExpansionBayHD/index.html
for the B&W G3
http://www.xlr8yourmac.com/G3-ZONE/yosemite/IDE/
in Your B&W G3 or G4 System
http://www.xlr8yourmac.com/IDE/IDE_RAID/driveinstall.html
http://www.xlr8yourmac.com/powerbook_g4/PB_G4_HD_upgrade/pb_g4_hd_upgrade.html
You should use a 2.5in hard drive with a max height of 9.5mm
http://www.xlr8yourmac.com/systems/powerbookG4_12in_HD_upgrade/PowebookG4_12in_HD_upgrade.htm