Everybody is a newbie to start with, a clean install is quite easy to do because you just follow the requests on screen.
This is the method for XP, I would imagine that windows Vista or 7 are similar.
This is going to be a bit long but here goes, first of all, I assume that you have a full version of XP with the product key,
!. start you computer and press what you need to press to get into the BIOS (my computer is F2 but many are different)
2. Once you are in the BIOS, you need to find where the list of boot devices is (use the arrow keys), this will say, 1st boot device is your HARD DRIVE, 2nd boot device, will be your DVD/CD DRIVE, you need to make the first boot device your DVD/CD player, so that when you re-boot your PC it will boot from the DVD/CD player and not the hard drive, I dont know what your Motherboard is so I do not know what you need to do to get to this but it is normally quite simple (if you have the booklet for your motherboard that would tell you) save the change that you have made put the XP install disk into the drive and turn off the computer.
3. now restart the computer and it will ask you to press any key if you want to boot from your DVD player, you have a limited time to press any key, if you take too long it will go past this option and you will have to restart it again, sometimes you may have to turn off the numbers lock on the keyboard but in most cases it will work straight away.
4. The install disk will start and you will be given the option of deleting the partition, you must delete it, usually by pressing D on your keyboard, follow the prompts at the bottom of the screen, after the partition has been deleted, the hard drive can be formatted, the prompts on the screen will tell you what to do, once the formatting process has started you will have quite a time to wait.
5. When formatting has finished, the XP will start to install, it will get so far and then ask you to type in the product key, do this and the process will continue.
6. At the stage when it is nearly finished, you will have to put in information regarding where you are for the time zone, Greenwich is the one for the UK and you will need to let it know that you want your keyboard to use the English version, not the American English because that is different to what we use in the UK.
The rest is just doing all of your installs for various applications.
It sounds quite daunting but it really isn`t but it does take a long time before you have everything done, I would say about six hours or more, I hope that I have not forgotton anything, the most important thing is to get your computer to boot from the XP Install disk. It has been a while since I did mine but I have done a few installs and I think that you will be OK, you will have to activate your copy of windows, otherwise after about thirty days it will not work properly, activation can be done when you are connected to the internet or by phone.
Good luck.