I need to know if this is the password in BIOS (the motherboard) or the Windows password. If it's the Windows password then use this utility. Burn it to a blank CD with IMG Burn portable and boot it. You can boot the CD by pressing the F12 key right as the computer boots. Now chose the boot from CD option. This will boot the CD instead of your hard drive. The rest are in the instructions from the website. Very easy and straight forward. I've used this tool before and it works quite well.
https://pogostick.net/~pnh/ntpasswd/
If you want to just wipe the entire harddrive and start over. You boot the operating system CD like I told you about using F12. The reset is self explanatory. I should mention that after the first run of the CD install procedure, it will automatickly reboot. DO NOT press any key to boot from CD again when it asks. You only do this the first time you boot the CD. Just let it boot and continue installing.
Buy this if you have a working product key on the side of your computer.
http://www.ebay.com/itm/Windows-XP-...073472?hash=item2372df03c0:g:9eMAAOSwOdpX0ty~
This might have the included product key.
http://www.ebay.com/itm/Microsoft-W...293677?hash=item41b065282d:g:F5cAAOSwIgNXrNwA
They sell it with RAM because of Microsoft's asinine rule that the operating system be sold with a piece of hardware. So people get around that buy including a piece of RAM that may or may not work. You can toss it.
Buy this if you have a Dell. In which case no product key is needed since it's OEM. What brand is this computer by the way?
http://www.ebay.com/itm/NEW-Microso...203218?hash=item2372c27a12:g:oMMAAOSwt6ZWVh7S
Here's another one that might have a product key. But I would ask the seller.
http://www.ebay.com/itm/Microsoft-W...769422?hash=item1a1b18f24e:g:OQIAAOSw3xJXnlmQ
I think your best option which should be the easiest is to use the Password Recovery CD and reset the password. But having a back up copy of XP doesn't hurt. Just make sure you download and install service pack 3 for XP.
For a good definition based anti-virus that is lightweight and won't bug you, use Bitdefender Free. You might also want to check out Sandboxie. That will help greatly on making sure ransomware doesn't get on the machine. No definition based anti-virus completely protects you against ransomware.
Please ask questions if you need help.
Edit-
that old HDD and whatever is on it is useless to you anyhow.
Noting this. After you get situated with the computer. Install the program HDTune and check the SMART info and test the drive. It's not a full proof way of making sure the hard drive is fit, but better than nothing. Sometimes hard drives just die without any SMART errors or known bad clusters.
If you do buy a new hard drive, clone with AOEMI Backuper using a PATA to USB adapter. You plug in the new hard drive to the adapter. The adapter plugs into the USB port of the computer and you direct AOMEI to clone to the hard drive on your cable. Then after it's done cloning put the new hard drive into the computer and it will be like nothing changed.
I've used AOMEI Backuper many times. Works like a champ and easy to use.