Are you using OS X or OS 9? I am also wondering if you formatted HFS or HFS+. I think that on the larger drives, you want to go HFS+ due to sector size. It is designed for the larger hard drives, and security and so forth.
Okay, I talked to WD on the phone and they said I need a controller card for the Mac to make it read the EIDE HD at its fullest capacity. Can anybody here give me info about controller cards, such as which kind will work in an old G4 tower 500MHz? I'd like to find something cheap on Ebay, if possible.
G4s before the MDD models only support drives up to 128GB in size, irrespective of the actual drive capacity. Having said that, it is possible to use drives bigger than 128GB in these machines. What you need is the latest version of Intech's SpeedTools (http://www.speedtools.com) which comes with a rather natty utility called ATA Hi-Cap. This allows you to use drives bigger than 128GB with these earlier G4s, with the proviso that you can't use a partition bigger than 128GB. In other words, you'll have to partition your 200GB drive into two partitions, neither of which can be bigger than 128GB.
I had this problem a few months back but once I applied this utility, I got back 70-odd GB from my new 200GB Maxtor. Now that LaCie are doing monster drives (the 1.6TB looks rather attractive), utilities like ATA Hi-Cap are becoming very useful.
Sounds to me like you're trying to put in on an older ATA connection that has a limit of 120GB/137GB. There is a size limitation on old ATA hardware. You may need to purchase a newer ATA/5 or ATA/6 PCI card to see the whole thing. Which version of G4 is this?