What do I have to back up before I re-install?

Personally, I never reinstall without taking a full disk image of my existing OS...onto an external USB drive usually so it stays out of the way of your reinstallation.

So many times, I have needed something that wasn't in the directories I would have manually backed up.

Good hard drive imaging software would be Acronis True Image or Norton Ghost.

Usually with these programs, you can browse through a copy of the image afterwards from your new OS and just pick out the particular files you need without having to restore the entire image.

• Password database (e.g. PasswordSafe)
• Accounting data (Quickbooks, ACCPAC, Pastel)
• Any important account / login details
  • Paypal
  • Online banking
• E-mails
• Calendar, appointments
• All documents (word processor, spreadsheet, presentation, PDF)
• Video, audio files
• Any media library databases (Windows Media Player e.g.)
• Serial numbers / details for unlocking purchased software
• Downloaded software
• Device drivers
• Browser bookmarks
• Databases (MS Access, SQL)

I recommend a program like SpaceMonger (there are free equivalents, I just prefer this program) which will scan your entire drive, and can present a list of all files by type. Then simply go through the file types that are important and you shouldn't miss too much.

As for registry settings etc, I haven't tried it, but it may be worth looking into the built-in files and settings migration wizard in Windows.

I backup:

• my drivers, making installing easier (and browserless)
• my antivirus installer!
• program installers that are worth re-installing (or download them again)
• program settings that only require copying folders
• documents/pictures and other random files that aren't on a different drive
• PST files so I don't have to redownload or lose email
• browser settings like bookmakers (yes yes I should get that done online!)

That's about it

Edit: thanks for the email comment