To see what (IDE) drives are physically on your system invoke:
ls /proc/ide
You should see something like "drivers hda hdb hdc hdd", where hda is your master drive on your first IDE bus, hdb is your slave on your first IDE bus, hdc is your master on your second IDE bus, and hdd is your slave on your second IDE bus. The files under /proc/ide/hd* will help you identify your files by model and physical size in case you are not sure which is which.
First you need to create a partition on your missing drive. Assuming that hdb is your missing file, you would invoke "fdisk /dev/hda" to start an interactive session with fdisk, and partition your drive. If you are not sure what you are doing, see this how-to:
http://www.linux.org/docs/ldp/howto/...ion/index.html
After you have created your partition, you need to create a file system. Assuming you want to use the Libranet default of ReiserFS, invoke:
mkfs -t reiserfs /dev/hdb1
Finally, create a mount point and mount your system, e.g.:
mkdir /data
mount /dev/hdb1 /data