A few comments :
1. linux driver CANNOT write to NTFS, only OVERWRITE.
2. There is a captive NTFS driver which use the native Windows driver(thunk/wrap in technical term) that can write to NTFS. This requires you to either detect where is ntfs.sys on the booting system or distribute it(copyright infringement)
3. it is not difficult to automate sensing the HD presence. Take a look at KNOPPIX's initrd and its init script.
However, I don't see why you need Xebian. Start with KNOPPIX would be easier if you want a full feature linux for PC. Afterall, you only need the script/program to do the lock/unlock for an Xbox HD. You don't even need FATX driver as that is not safe in 2.6 kernel which is needed for lock/unlock.