Change the jumpers on your cdrw and dvd drive as we mentioned in your "hardware' post.
Put the XP cd in the drive,choose boot from cd as first boot option,hit any key to boot from cd when prompted.
After XP's cd does it thing,click on install,XP will ask(should)would you like to repair or install,click on repair,XP will fix the existing installation.
Note:As you run the XP disk,an initial screen will appear with a repair option,this is for the XP console,that isn't what you want,unless you have advanced knowledge of the console,what you want is the option to repair offered after you click on install,if the option doesn't appear,reboot and try again.
Removing the acpi function may not be the best option with XP!