If your using XP as your operating system, the drive will not be seen until you format it.
Right click on your "My Computer" Icon, choose "Manage" then disk management from the new window that appears.
The new drive will be shown in there. Right click on the drive in the right hand pane and choose format, follow the on-screen instructions and format the whole drive as one, or partition as you require. It will now show in your "My Computer and be ready for use. j.
Set your hard drive to slave and reboot you should also go to the bios and enable OS2 as you will be running more than 64meg of ram i have done this on my older computer if i am wrong someone will correct me.
Set your hard drive jumpers to slave and connect to IDE 0 cable: then go to the bios and set the ID0 0 slave settings to 'AUTO' or to the HDD settings for cylinders/heads etc ( this is usaully on the HDD information sticker on the HDD ) save & exit the bios.
The PC will then reboot and you should see both drives on the 'Pre Windows' Display (you will only have a few seconds to check this) then once in win98 you should see both drives in the Device manager (probably 2 type 47's)