Hi there,my understanding of the problem is that it is actually better to enable AHCI after you have installed Windows XP. This item might prove helpful: http://expertester.wordpress.com/2008/07/27/how-to-enable-ahci-windows-xp/
It is often a problem when trying to run IDE and SATA devices on the same system. I would just advise you to purchase a SATA DVD drive instead. They are so cheap now that it really doesn't make sense stricking with your old one. I just bought a 24 speed DVD RW from Ebuyer for under £12.