if you are talking about a REV A B+W g3.. i would highly reccommend an alternate mac-bootable hard disk interface, such as a pci sata card + new sata drive; at the very least get a PCI IDE ATA addon card, because its going to be leaps + bounds faster than the original IDE interface on the motherboard.. it just sucks!! its not very fast at all. like u will be lucky to get 20MB/s consistantly, its a waste to try to run any hard drive thru that ide interface! i used to use an Acard 6880M card that was also a raid card... has 2 IDE ports on it that can each take 2 devices..
theres a huge performance jump between going from Ultra ATA/33 to Ultra ATA/133 (or SATA/150)
like do the math:
133-33= 100
thats how much MB/s you have to possibly gain.. which modern hard drives can do just fine
get a sata/ide adapter, and a pci-ata or pci-sata card.. and enjoy your awesome macintosh at its best
it wont actually do 133 but itll do a whole lot more than 33! (otherwise your g3 will be stuck struggling to maintain 20MB/s)