Reinstall of XP would cure the Service Pack 3 problem but then you would have to track down the SATA drivers and have them ready on a floppy when the install calls for them. No idea where you would get SATA drivers from though.
Service Pack 3 is essential as there is no way of installing many of the later security patches without it and as XP isn't the most secure of operating systems anymore you really don't want to be connecting to the net without SP3 and all updates.
You could try pulling the CMOS battery and letting it sit for a few minutes to see if that clears the CMOS and also the password. There may also be a CMOS jumper which you can use to do the same thing but you may need the motherboard manual for that.