Have you set a partition on the disk yet? You won't be able to format it until you do so.And since you mention that it shows up in "My Computer", can I assume that it is a secondary disk? Is it eventually meant to be the primary drive?
Since you didn't mention what your OS was, here is a reference from Microsoft for XP:
http://support.microsoft.com/?kbid=313348 Just ignore the intro stuff if you are not formatting a primary partition, otherwise the rest of the instructions are the same.
This is another helpful, all encompassing tut:
http://www.bleepingcomputer.com/tuto...torial116.html