Fortunately re-installing the OS is not windows dependent so the issues you are having now will not affect doing a clean install. Just to re-itterate.......Doing a clean install will wipe all of the files from your PC if you do not have a backup of the files they will be lost.
First look at you CD's that came with the computer. Do they say Restore disk or Windows XP Media center? Is there a disk that says Drivers? More than lkely you will not have internet connectivity after the install without having the drivers for your network card so if you don't have that download them from HP, preferably on a computer other than the infected one.
Okay now you can begin. Start the computer and enter the BIOS which you will see as the computer starts. Typically it is the delete key but it can also be the tab key, or F2 key. Do not change anything in here other than what we are looking for. Scroll through the menus till you see something that says something like boot order or drive boot order. You will want to change the order so that the CD-ROM (or DVD) is listed first. It is fairly straight forward just follow the directions given on the side or bottom of the screen for what buttons to push. Save the changes and exit. The computer will restart. When prompted hit the key to boot from CD and the windows instalation will start.
Most of this is pretty straight forward so I will take you throught the important parts.
After you accept the license agreement choose to install windows. Where it asks you to choose a partition to install to you want to delete the current partition, create a new partition, select that partition to install to, then do a quick format.
At this point go eat lunch
it will take a little while. The computer will re-boot and you will have to do a few tasks at different times. Computer name-this can be what ever you want. ALWAYS set a password on the administrator account(preferably one you can remember and that isn't a full english word). You will have to enter your windows product key which is on a label on your PC somewhere(top or side), choose your time zone, and make sure the system time matches the real world.
Everything else you can just click next on and you will be fine.
After the install is completed the PC will re-boot once windows is started install your drivers and make sure the firewall is up and running. Then head immediately over to windows update and download all of the updates, service packs, and hotfixes of the critical type available. You may need to do this more than once since some updates are dependent on the updates you just installed.
Now install your antivirus, programs and restore any data you may have.
For the restore disk you still need to do the BIOS check, start from the CD and then just follow alomg with the wizards.
PPhheewww....let me know if you have any question or concerns.
Get your facts first, then you can distort them as you please.