Well, you seem to be not having fun there.
I posted the KB link to your prior problem.
Now, I should ask you. What  led you down the path to reformat your HD?
After rethinking your changing the drive letter problem, I remember why I won't buy another prebuilt PC.
HP, Dell, and other mass PC marketers build systems that their support teams can answer questions off their que cards. Nowadays, they'll have the recovery disk hidden inside your HD. That could be the problem to question no. 1.
The recovery section on your HD, is considered a hidden active partition. You can't see it when running Windows, but it's there. When you reformatted HD, that hidden, became the new C:\ drive.
You didn't mention if the WinXP Pro, was original, or upgrade.
If you can do this on your own or not, and have friend with high speed internet and a CD burner, than I can offer a choice.
knoppix.com
This will allow you to burn a LiveCD. Choose the closest mirror to your locale. You reboot PC, and if you have CD booted first, through BIOS. You'll be greeted by a penquin. Just like Windows, in the bottom left is a Start button. Find qtparted. 
This is not for the faint of heart. Once you commit, it's said and done. Once qtparted is running, for a true format, undelete all partitions. Then set up space in undeleted section. Give C:\ 10 Gs, then allocate rest as you see fit. Commit your changes, you'll need to reboot for changes to be written to HD. Maybe option will be available, if not;
Start button that doesn't look like start button, Logoff, reboot.
If you have a retail or OEM WinXP Pro, not an upgrade, you shouldn't have any problems.
Remember this, unless it's required by Microsoft, then place it in  D:\Program Files. Your defrags will love it.
 -------------- Original message ----------------------
From: Diane Kroeckel <[log in to unmask]>
> I have an HP a410n computer.  It came with Win XP sp1 Home edition.  The
> restore disks they gave me didn't work and they said it was my
> motherboard and I needed to bring it in.  Instead I decided to load a new
> copy of XP SP2 Pro.  
> 
> Now my computer says I don't have an Audio Device.  So when I try to
> install the HP driver, I get this error.
> "you must be logged on as an administrator to install this update. Update
> has been cancelled. (9999)"
> 
> I even logged on as Administrator, but got the same error.  They say that
> I can only run the version that came with my computer.  Is this true?
> 
> Diane Kroeckel
> 
>                          PCBUILD's List Owners:
>                       Bob Wright<[log in to unmask]>
>                        Drew Dunn<[log in to unmask]>

                         PCBUILD's List Owners:
                      Bob Wright<[log in to unmask]>
                       Drew Dunn<[log in to unmask]>