You need to create and format a partition on the disk before it will be available for use.
Right click on My Computer and pick Manage, in the new window pick Disk Management from the left hand menu, the snap-in will open on the right. Locate your new disk in the right hand pane (it'll show as unallocated), right click in the space and pick New Partition, give it a label if you want, check the Quick Format box and hit OK. It takes about 20s to do a quick format after which Windows will give it a drive letter (you can change them around if it ends up after your DVD or anything else).
It should now be available in My Computer / Explorer.