Is there any way to edit the global address book in Exchange from a 98 client machine?
The easiest way isn’t the way you’re expecting. I’d use a remote-control solution like PCAnywhere—or better yet, VNC—to do it.
Basically, you just install the host software on your Exchange Server—be sure to set up the security and passwords—and install the client software/viewer on the workstation from which you want to edit the address book.
Whenever you need to edit the address book, just fire up the remote software and take control of the Exchange Server. Just like sitting in front of the console, but you do it remotely.