Disk Encryption/CD Boot

I have a user who has corrupted WinXP Pro system files. To resolve, I typically boot from the XP cd and run a repair. However, this user has 3rd party disk encryption software installed which requires pre-boot authentication. As soon as the credentials are entered, it boots straight from the HDD with no option to boot from CD. Now, if you login and then hibernate, you can turn the laptop back on without having to enter the encryption password. Is there a way to boot from a CD after coming out of hibernation? Is there a file I can edit that would point Windows to load from CD rather than HDD? Any and all suggestions will be greatly appreciated. Thank you.