I doubt flashing the BIOS would help.
The system BIOS contains all sorts of information for getting the system started, The RAID part of it is just one small section.
Flashing the BIOS with the latest RAID image will probably render your system unbootable!
you should be able to have the O/S on one HDD conencted via a 'normal' IDE channel and then have the data on two drives combinbed as RAID 1 - that will give you redundancy and NTFS will give you security (If it's configured correctly).
What sort of security are you after? There are many levels for PC/Server based systems.
If you are trying to do something specific security-wise then let me know - It's what I do for a living!
Gary.