How can I back up my computer to an external hard drive.

What program do you plan on using to back ip up?

There are many programs that can do a full system backup.

I use CNet for a lot of my info and the following link is software that they have reviewed and rated and allow for download or purchasing.
Backup Software - Reviews and free downloads at Download.com

Rick

Also, Windows has a built in System Restore and Backup Utility. It's in- All Programs-Accessories-System Tools... If you use the Windows Utility, make sure your ExHDD is plugged in and recognized. When you click backup now it will ask you were you want to back it up to. Click on the drive letter corresponding to your ExHDD. It will backup to this drive.

As ITstudent2006 mentioned Microsoft has a backup, the following site explains how to:

Windows XP: Format backup drives with NTFS

Check out the following also:

How to Back up Your Computer Files | eHow.com

Backup Your Hard Drive with an External Storage Device

Use ntback command in run menu and select all that you want to backup and provide destination i.e. your external hard drive location.

Use a 3rd party software like Symantec Ghost or Acronis True Image to create fully recoverable back ups of your computer.

Read more about it here - Creating Backups - Helljack6.com

If you have external a good free one is Cobian backup Google it :)
But a lot of externals come with there own software for backup.
Example.
Maxtor one touch
Seagate free agent
ext..