If your PC is running fine on the old hard drive you might consider cloning
the old drive to the new drive (some hard drives come with a CD
that may have a utility to clone/migrate your OS to the new drive without
the
need to perform a "Clean Install")
With a "Clone" from the old drive to the new drive:
All you files, settings and applications will be in place and usable.
However I recommend burning your data files to a DVD
before you start as just in case.
However if you are determined to do a "Clean Install" then read on.
Do the clean install with the old drive disconnected.
This assumes you have a XP CD that came with you PC.
(See notes below)
Before you do the move to the new case and hard drive:
Make sure you have the drivers you need for your motherboard, video
card, sound card, Etc. Get the drivers from the HP web site if needed.
(Download and burn them to a CD)
Then run Belarc Advisor:
http://www.belarc.com/free_download.html
It does a good job of providing a wealth of information
including software Key codes.
Also before starting the Clean Install:
Verify your CD Key code matches what Belarc Advisor reports
for your existing installation on the old hard drive.
Note: OEM Windows Installs usually come with a Key Code sticker
on the PC case and may not match the factory installed key
reported by Belarc, so use the code on the sticker.
Note: A number of vendors now supply restore CD(s)
or have a restore partition on the hard drive and usually
do not supply a Windows XP CD, so the instructions below
may not apply.
How to do a Clean Install of Windows XP:
Start by changing the BIOS setting to Boot from CD drive first.
Then see the web sites below for detailed instructions:
From Michael Steven's:
http://www.michaelstevenstech.com/cleanxpinstall.html
more info:
http://windowsxp.mvps.org/XPClean.htm
and:
http://www.theeldergeek.com/clean_installation_of_windows_xp.htm
also:
http://www.bootdisk.com/
With a "Clean Install"
You will be able to move your data files to the new hard drive, although
I suggest burning these files to a DVD before you start the move to the
new case.
You will not be able to move the applications, they need to be reinstalled.
Do make sure you have all the application CD(s) and the Key Codes for
each CD before you start.