XP can see NTFS and Fat32, but ME can only see FAT32
If the slave drive is NTFS, it will be visible in BIOS and ME as an unformatted (unreadable format) drive, and therefore cannot read the FAT (file allocation table) which includes the drive size and drive letter (which is variable for XP)
Something like Partition Magic may be able to covert the drive from NTFS to FAT32 without formatting the drive