Where can I can get new drivers for hard drive?

I assume that you've Installed the configuration jumper on the Seagate hard drive as Master with Slave Present. You don't need to install drivers, but you do need to boot your iMac from the OS 9.1 CD and locate "Drive Setup" in the Utilities folder. When you run the program to format the Seagate hard drive as a Mac OS Extended (HFS+) volume (or volumes - if you'd like to partition it), a hard disk driver will be written to it. An iMac G3 won't recognize any formatted hard drive that's larger than 128 GBs, so be aware if you've installed a 160 GB or larger drive. There is a software workaround (Intech's "SpeedTools ATA Hi-Capacity Driver") that involves a partitioning scheme, but you must buy the Intech software.