If its IDE it will run in a B&W G3. There are two limitations: There is an absolute size limit of 128GB per drive. This means the biggest drive you can put in it without a PCI ATA controller (or SATA controller) is 120GB, as anything bigger will only show up as 128GB.
You can run a hard drive safely on the optical drive's IDE bus, but it is slower than the ATA.
Not all rev 1s do this. Some are awful, others are rock solid. Using drives bigger than the stock 6, 9 or 12GB ATA drives.

The 128GB limit can be bypassed with software called Speedtools. I haven't tried this, but I don't really trust Disk Utility implicitly when it comes to partitions. I cannot imagine a drive formatted this way will be more reliable in terms of software errors.