Dropbox

[steve.ledger]

Backup is a term applied to many things.
You can use file syncronizing backup tools which create copies automatically based on rules or a complete system image which can be used to restore your entire OS, programs and files in case of a more irksome disaster.

Here's how to use Windows XP backup
Vista Backup & restore and Windows 7

How much room any of this requires depends on the size of the data being backed up or the size of the entire partition you are creating a backup image of.
Rather like that how-long-is-a-piece-of-string question

[michaelbuddy]

I remember a couple years ago there was a utility that let you and a family member say in a different house, use each other's PCs as backup locations. It would constantly be synching a protected copy of part or all of your drive storage. I wish I could remmeber what that was, as it would be the perfect solution if encrypted.

[gnurf]

I'd say an external hardrive is the best thing, and then there is a really neat and simple backup/synchronization free tool from Microsoft called SyncToy.

You can also use harddrives that can be connected to you home network so you don't need to have it "plugged" to you computer all the time.

I use Dropbox and it really useful for sharing files between your home and work, or with your clients, but the diskspace is only 2 GB for the free version, not very useful for backup.

[handrawn]

as a very rough rule of thumb to the length of a piece of string, an acronis image backup of my XP [system only] is currently 3.7GB

[jvila]

Nancy,
I'm always use norton ghost to do that or convert your machine to a virtual one using vmware converter and you will be able to start your machine in minutes in any other hardware that has installed vmware.
Anyway, in your case I'll use Ghost.
You can do an image of your disk and use it to restore it on other disc or using ghost explore you can open that image and see/extract files from it.
If you need more details don't hesitate to contact me.
Best regards

[steve.ledger]

There are so many backup and partition image tools around (even free), I think it all comes down to the one that you understand best and works well for you.
Whatever you choose will be better than doing nothing

[MEB]

Burpee,
Dropbox isn´t adequate for backup purposes. As gnurf already said it only provides 2Gb (free account)and it´s not intended for full system backups, but to give you a way to synchronize files between computers and/or smarphones and similar devices no matter the platform (Linux, Mac, Windows).
An external drive (USB, Firewire or eSata depending on your system available interfaces) or a NAS (Network Attached Storage) will be your best options.