Gunsmith: the most critical stuff most people own is their EMail archives and their word processing documents. Some people are into spreadsheets, etc. Any document you've spent time working on matters.
Browser bookmarks are important for some folk.
Then there's "lesser stuff" - games that could be reloaded but you'd lose all your saves, cool videos you've downloaded, stuff you don't WANT to lose but it wouldn't kill ya.
A "whole disk backup" like via the method I pointed to is the safest.
A related point: in Windows, every file has an "extension" (last (usually) three letters at the end after a period) that tells Windows what type of file it is. For example, the code for MS-Word documents is .DOC, Excel spreadsheets is .XLS, and so on. Every type of data file has a code. If you rename a file from something.doc to something.xls and then double-click it, Windows will try and stuff the file into the Excel spreadsheet where it will choke and gag (you'll get an error basically adding up to "Excel doesn't know what the hell to do with this alien weirdcrap you're feeding me"). Windows also matches the data file icon to a program if that program is available, so anything named .DOC usually gets the icon for MS-Word if that's available or if you're using a free clone of word, it will be Abiword or OpenOffice.
Windows XP has this STUPID "feature" where by default, it hides this "extension" from view. Open up "my computer", open a hard disk icon, then in the menus (under "view" I think) there's a series of settings for "view options". Find that, UNcheck the box that says "hide file extensions of known type". EVERYBODY, for the love of God go do that. Yes, right now.
The system will then show you what the file types are for your document files. You can then use the Windows "search for files" function to look for those extensions (search for "*.extentioncode" without quotes) so you can see where your critical stuff is - what folders they're in. Most people have no clue where their stuff actually resides.
Once you KNOW, you can figure out how big the stuff is in total and where to grab it from.
If it's smaller than 700 megs, congrats, it will fit on a CD-R disk. Back it up by burning it to CD. If it's 4.7gig or less, it will fit on a DVD-R. So do that.
If it's like mine, up around 25gigs, bite the bullet and go buy an external USB hard drive, as big as you can afford. Back it up to that, like I do, either by hand-copying stuff (now that you know where YOUR stuff is), using a backup utility such as what the better USB hard disks by Seagate, Maxtor, Western Digital or others ship with, or by using the Gparted-Clonezilla disk I mentioned.
With the latter, you download a "disk image" file of about 150megs, file extension is .ISO, and you turn that into a complete CD boot disk. If you have any commercial CD burning software, it will know what to do with an .ISO file and will prompt you for a blank CD. If that doesn't work, free ISO reader/burner programs are available, drop me email at
1.jim.march@gmail.com and I'll go find one for you at tucows.com or similar.
Once you have the burned disk image, you tell your computer to try and boot first off CD (or DVD), second off hard disk if that's not available. You then put the GParted-Clonezilla disk in, do a normal restart and it boots a simple, specialized Linux install that is only useful for backing up data (even a Windows disk) or fixing Linux disks. It's a breeze to use.