It's a disaster: your PC is trashed and you'll need to reinstall everything. That should at least be possible with Windows and your applications, because you've probably kept the original discs safe somewhere - but what about your drivers? Even if you can find the original driver discs, they won't include any updates, so you'll be forced to manually relocate and reinstall each of these before your system is back to normal.
Prepare yourself with Double Driver, though, and it could be a very different story. Run the program and it'll detect and list all your drivers, selecting those that aren't from Microsoft. Then click the Backup button and it'll save them to a folder, ZIP file or self-extracting executable, which you can safely store away on a CD.
And then, if the worst happens in future, just pull out your backup disc and launch the copy of Double Driver it contains. The program can then restore your drivers in a couple of clicks, with no further web browsing or downloading required.
Double Driver can also print your driver list, useful as a troubleshooting tool if you do it regularly. If you notice your PC seems slow, unstable or has some other problem, for instance, just print out the driver list, compare it with last month and look for any change: driver bugs are responsible for many PC issues, and this just might offer a clue.