It really depends what you want to backup. If you want to make a complete backup of the whole system (OS, Programs, and Data files) then I recommend using Acronis True Image. This makes an "image" of your hard drive and puts it elsewhere. This is a pay-for program, and in my opinion is worth the $$$. In the event of a failure you can just copy everything using the Acronis program to a new hard drive and it will boot straight back where you last backed up with the program.
There are also programs that backup all your data for you, meaning in the event of a failure you will need to install the OS, your programs, and the backup program and then you can use it to restore all your data. For example, Nero also has this feature included in the Nero BackItUp program. Alot of people have Nero, but don't actually know it's there. The benefits of this kind of program is that it compresses all your data, making it fit smaller on the source.
Otherwise you could just copy all your important data files over to the backup drive, this is what I currently do. I have a single external hard drive and once a week I copy all my important data files straight over, because personally I'm not phased at installing XP and all my programs again. I have done this many times...
And as for actual hardware to use for the backups, I'm not too sure what would be most cost-effective for all three computers. I imagine something like a NAS (network attached storage) device might work, but I've never used one of these before... I'm sure someone else will comment on this soon, though so just wait and see what they say.
Oh and YES this is important!!!! Glad to hear you wanna know about it!
EDIT: Online backups are also good, but the biggest drawback is that you have to upload everything with your internet connection. Even with a fast broadband, if you have GB's of data to backup, it will take a long time... And then you'll have to download it all again. This may affect your ISP download/uploads, and therefore, your bill ($$$$)
Edited by ruthandtroy, 15 July 2007 - 12:37 AM.