You have not told us your distribution (this helps us to help you, please update your profile!)
I do not know a GUI way of doing what you want, but the command line is easy to use.
I have never used "Partition Magic", I just use fdisk. First, you need to have a look at your disk to make sure it is the right one, and partitioned as you 'd like it. I am assuming the disk you want to format is /dev/hdb. So take a look at it (You will have to be root to use these commands):
fdisk -l /dev/hdb (That's a lower case "L", not a "1")
Do the partitions look right? If not, maybe you should be looking at another disk eg /dev/hda. Choose which disk/partition you want to format. Be very careful here, if you format the wrong partition you will be in big trouble (lost data)!
Now you need to choose a filesystem. I use ext3. So if I wanted to format /dev/hdb1 as ext3, the command is:
mke2fs -j /dev/hdb1
See man mke2fs for more detail.
Edit: As it is your EXTERNAL drive, it is probably /dev/sda
Last edited by tredegar; 11-30-2005 at 11:51 AM.