An excellent idea, & something I wish more people would do instead of coming to a forum and panicking with "Help, my hard drive has died & all my files are on there!"
Since you have a laptop you cannot fit another drive next to the existing one, so you'll need to buy a 2.5 inch external hard-drive enclosure & fit a new 2.5 inch hard drive into it (all laptops use 2.5 inch drives, so when required you'll be able to put this drive inside your laptop).
Then you will need some "drive cloning" software which copies exactly the contents of your laptop drive (including the boot files) to your external drive.
I use "Active@ Disk Image" so that's the only one I can confidently recommend. The details are here, as well as the full user guide (for your needs, read section 8 "Clone Disk Wizard"
Alternatively, using the same software, instead of cloning one drive to another, you could create a "Disk Image" which creates a large file on your external drive, which can be written to a new drive inside your laptop when the need arises. For more info on that method, read section 3 "Creating a Disk or Partition Image"
and section 6 "Restoring a Disk Image".
Like I did, you'll probably find it all a bit daunting at first. But stick with it & you'll find it easier to understand eventually, as well as it giving you the peace of mind knowing you have a rescue plan in place!
Edited by phillipcorcoran, 25 April 2011 - 09:01 AM.