I agree with the start of your plan, with a caution. Once you have a backup made, VERIFY it to be sure that you actually can restore all of your stuff from it. I have seen disasters when a backup file failed to work.
From there on I suggest changes.
2. Do not change the BIOS settings yet. Use your Intel storage utility to delete the RAID0 arrays. Yes, plural. You have TWO called C: and C:, apparently created on the same pair of 1TB units. Use the Intel utility to get rid of them.
3. After that you can go into BIOS Setup and change the port mode. To what? That depends on your OS you are installing. If it is Vista or Win 7, set to AHCI. If it is XP any version, easiest to set to IDE Emulation unless you want to get into loading an AHCI driver from a floppy disk.
4. Before installing I recommend you connect only ONE HDD. Leave the others for later. When Vista or Win 7 Installs, it looks for a second HDD. IF it finds one, it establishes a hidden Partition on it to save a copy of critical files that can be used later in a disaster to restore the full OS on the first disk. BUT this means that your second HDD MUST be in place at all times, or the machine cannot boot! On the other hand, if there is only one HDD present, the hidden Partition AND the OS will go onto the same HDD. (I know, doing it this way defeats some of the safety inherent in the first plan.)
5. Install the OS to the only HDD in place - you indicate it will be one of the 1 TB units formerly part of your RAID0 array, but now just a stand-alone HDD.The Install process will create the new Primary Partition needed (and this writes a new Partition Table, replacing old info about a RAID0 structure). If you want to make this a smaller one with only the OS, and plan to install all your applications and data files on a different Partition, NOW is the time to do that. Make your first Primary Partition for the OS the size you decide - maybe 50 GB, or whatever is best. Do all of your installation and updating this way.
6. When you have Windows operating, use its Disk Management to Create from the remaining Unallocated Space on that one HDD a second Primary Partition (not bootable) that uses up all the rest of that HDD, and Format it by installing the NTFS File System. This will be a data disk.
7. Now install / connect the second 1 TB old HDD and use Disk Management to Create and Format a Primary Partition on it for data, too. It may be the whole HDD, or you may decide to make more than one Partition on this second HDD unit. Either way, the Partition(s) do NOT need to be bootable. In doing this you write a new Partition Table to that drive, replacing any old info about its former use in a RAID0 array.
8. Now install / connect your third HDD, and set up its Partition(s) in the same manner.
9. Now you have three HDD's installed, containing four (or more) Partitions, each named with its own letter and treated as a separate "drive" and ready to use. The first one is your C: drive that you boot from.
10. Within Windows, establish where certain key system files are to be located - Page File, My Documents, etc. It can be an advantage to place the Page File (Virtual Memory) NOT on the same HDD as the boot drive. That way access to those two frequently-accessed resources will be split between two physical units and be marginally faster. That is, it should be either on the SECOND 1 TB unit or on the 2 TB unit.