For the Drive?
If it's not there or reported as a smaller size the BIOS can not support that big a drive so you need to add a PCI-IDE Card so you can access the HDD.
Also is this HDD formatted? As you want to delete the contents I would say so but what Partition Type is in Use? 98 can only read FAT 16 & FAT32 Partitions and not NTFS so Windows is working correctly if that is the case. Provided that you can see the full size of the drive in Computer Management you can format it there or you can do it from DOS from either a Floppy that you make from Windows for the Format S command or from a CD if you don't have a floppy drive.
The Ultimate Boot CD has a Formatting Utility on it if you don't already have a CD made up to do this.
http://www.ultimatebootcd.com/download.html