A windows monitor, mouse, and keyboard will work on most older Mac computers. However you really need a Apple keyboard because there are some different keyboard keys your gonna need like the Apple and Option key that a windows keyboard doesn't have.
As far as the hard drive I work mostly on windows hardware so someone like BDAqua would be very knowledgeable with that. I seem to think you need the hardware drivers for the G5 that may or may not be with the new OS 10.5? A Dell hard drive will not work with the G5 if it already has a windows OS installed to it, you'd have to reformat the Dell hard drive while in a Dell computer to erase it. Your not wasting your time.
Put a new 1 terabite hard drive and got new osx 10.5. Having trouble installing the osx.
The newest, 6.0 Gbps drives don't all automatically work with the G5 1.5 Gbps controller. Most Hitachi 7K drives are reported to, but Western Digital SATA 6.0 Gbps drives require a jumper on pins 5 and 6.
Similarly, Seagate drives need to be limited to 3.0 Gbps by jumper.
No drivers are necessary for hard drives. All necessary drivers for hardware are in the OS.