Ok, so you just took for granted, that the original hard drive was bad, because you got the "no operating system was found" error. Do you know how to get into the computer's BIOS, and see if the hard drive is recognized? Do you know how to clear the CMOS? Do you have the original Win98 install CD?
Do you have a Win98 bootdisk? If no bootdisk, download one here:
http://www.bootdisk.com/
If you boot from the bootdisk, and then enter the C: prompt, and then type "dir" (without quotes), and it will list the directories, on the new hard drive, and you should be able to see, if there is an operating system, on the new hard drive.
If there is no operating system, put the original hard drive back in, and see if that shows up in the BIOS. If it doesn't, check your cable connections, try another ribbon cable. You might try clearing your CMOS, or perhaps, your battery may be bad too.
Well, let's see what we have from here, before going any further.