All of the advice you've been given so far is excellent.
If I want to do a clean install, I spend far more time getting ready for it than I do actually reinstalling.
First I burn all of my personal data to CD or DVD-- and I make 2 copies of each one. The reason for this is that it is possible for a single copy to fail. It is far less likely that both copies will fail. This has saved my data repeatedly, so it isn't paranoid. The one time I failed to make 2 copies, guess what happened? It was a year before I got that data back. I learned to practice what I preach!
Do not drag and drop. The way I do it is I get a piece of paper and a pen or pencil. I open my burning suite and get set up to make a CD or DVD image (not the disk itself yet). I begin putting my personal data onto the screen where you prepare to burn (read your own software's help files if you want to know how) and I write down what is going onto this disk. I try to get it one folder at a time, but your data may not be organized into folders so I leave it to you to decide what goes on each disk. When I have what I need for one disk, I "burn" and image and call it 01. If I have a lot of data to deal with, I then make a folder (you can call it anything you like, just as long as you remember that it contains the data you've already dealt with) and I drag the data I just "backed up" into it to get it out of my way. I then repeat this process until I have all the data burned onto disk images.
Don't forget when preparing these disks to include all data. This means that you will have to find out how to back up your email, if you store any on your computer; your address book; your favorites or bookmarks; and any data associated with any applications. For example, you can find out how to back up and restore Outlook Express email and settings from here:
and if you have any applications that use personal files (such as Roboform, a recipe application, or another similar situation) you will need to find out how to back up those files as well. Give it some time and think about it. You don't want to have to rebuild all of this.
Once you have all of this done, burn and verify 2 copies of each disk.
Next, you research your computer. Belarc Advisor is a great help when you do this. Write down all of the applications on your computer. While you're at it, write down any hardware that will need drivers. If there's anything you want to leave out or add in, make a note of it.
For applications that you have the installations CDs for, go and gather the CDs and any necessary information for installation (such as a CD key or serial number). For free software, make a folder and download the latest versions (or the versions you prefer, if the latest aren't what you want). For any applications you have bought online and downloaded, find your original information (usually the confirmation email you received when you first bought it) and research how to reinstall the applications. You can usually download the program and then use the information you were sent to activate it, but make sure. Put that information in a folder, as well. If you have to, make text files of the activation numbers, so that you can easily copy and paste them in when you reinstall.
Gather any drivers you need. If you are downloading the drivers, put them in a folder as well. If you have commercial programs that you do not have CDs for and you cannot download them or get them some other legitimate way, you are out of luck. Make sure you know exactly how you are going to reinstall everything, because after the drive is wiped clean you can't go back. Take all of the folders and associated data you have gathered and burn 2 copies to CD or DVD. I don't put this on the same disks as the data backup because it can get lost easily. I need one known good disk containing this information to put with my installation disks.
This isn't all of it, but it does give you a good idea of how to prepare for a clean install. Take your time, think about what you need to do, and keep all of the necessities at your fingertips and you shouldn't run into problems that can't be solved.