First you have to partition the disk, and then run mk2fs on those partitions. fdisk or cfdisk will make the partitions, while mk2fs makes the filesystem on those partitions Assuming you are certain that this hard drive is /dev/hdb, which means you've made it the slave on the primary IDE channel:
This should show however many Gb of empty space: chop it up into partitions, make sure to give them the label either Linux or Linux Native (means the same thing), then run mk2fs on say /dev/hdb1
From there you're going to have to mount the partition, and then add a line to /etc/fstab so you don't have to mount the thing by hand every boot. Its pretty intuitive after that first bit.