depends what you want backed-up. If it is the operating system, it could get messy.
If you have a big enough external HDD I would personally copy every folder into a specific folder and leave it to do it. Or in an empty HDD into the root directory.

Then at your leisure delete things you weren't going to use. Like "Programs", "RECYCLED", "System Volume Information" but go searching for Fonts and keep them just in case you acquired them and need them for docs or spreadsheets etc. within "Windows" before delting that folder.

"Documents and Settings" will not have much you need, but keepr "My Documents" there will be loads of stuff you dumped there through lack of any time at the time.

Go searching for Fonts and keep them just in case you acquired them and need them for docs or spreadsheets etc.

That way all the folder structure is as you remember it. Files where you remember them. And modern HDDs are cheap enough to accept there may be duplicates. Use the HDD as an archive , NOT as a workhorse in case duplicates exist and you can't remember the update level.