What do you mean by "Windows 98 reinstall disk"? Do you have a restore/recovery CD or do you have a Windows 98 CD(full or upgrade version)?
You need a startup floppy disk that has the proper files in it before you try to format the hard drive. Go
here and click the "Windows 98 boot floppy image" link. Once the
win98_img.exe file has been downloaded and saved, insert a blank floppy disk in its drive. Double-click the file and allow it to extract its files into the floppy disk. Once that's done, you'll have the proper startup floppy disk that you'll need.
----------------------------------------------------------------