You are right. Not easy. The new hard drive needs to be Fdisked and formatted first before it can be used.
Download a Win 98SE boot disk from click here
Make sure the computer boots from the floppy disk first. Go in to the BIOS and change the boot order.
Once that is done switch off and then reboot with the boot disk in. When you get to the A:\ prompt type in fdisk and press enter.
Follow the prompts. When the disk has been fdisked you will need to reboot (still with the boot disk in) and then when you get to the A:\ prompt type in format c: and press enter.
When that is finished you will need to re-install everything from the original disks again.
ie. Operating System, motherboard drivers, Sound, etc and all programs that you had on the old hard drive.