One last one word of advice : your external USB HDD will probably come with a partition formatted in "FAT32" format, which is much more sensitive to any brutal halt (power failure, computer crash, ...). You should really convert the partition in NTFS format. But only if this HDD is for use with XP, 2K, NT, Vista, etc. If you have a Mac or a Win98 computer, you should leave as it is.
How to convert the partition : no need to reformat anything, you can perform a non destructive conversion like this : Open a command window : Start/Execute/ type cmd + return
type the following command :
> Dir Y: (Y: is the letter under which your new HDD is recognized)
Note Y: Label
> convert Y: /FS:NTFS /X (Y: is the letter under which your new HDD is recognized)
You will be asked a confirmation by entering the Y: Label
Convert will then make a quick check of the current file system, then convert the drive in a few minutes. Et voilà !
One more thing : with your new drive will probably be packaged a backup program (file backup at least). If not, check the drive manufacturer website, for example Western Digital. In most cases, these manufacturer allow end-users to download an OEM imaging software, which they have rebranded. So you might get a free imaging software quicker than you thought.