I don't understand where your problem is?
Yes you can have your OS on one drive not part of the raid and four drives in RAID 5, to do this you must set you SATA to RAID in BIOS before installing the OS on the one drive and you will be needed to preinstall the RAID driver during the F6 Windows setup even on the one drive.
What Motherboard do you have?
I know this is an old post, but just to extrapolate a bit on the previous posts -- they are correct, but some small detail was left out.
- Often, motherboards do not allow you to set the "drive mode" on a drive-by-drive basis, that is... to say, IDE emulation, AHCI, or RAID mode. Often it's one setting that applies across all drives -- even if they are not included in the array itself... they are operating under RAID mode.
- That being said, if it is Windows XP that is being installed, they are correct, you must hit F6 during the initial blue setup screen for XP. It will tell you to hit F6 if you need to install additional drivers. This will appear as it is loading all the generic drivers, before you get a chance to select the install drive/partition, etc. Unfortunately, the RAID drivers will have to be loaded via this method. Via floppy disk... which could pose a problem to some. Note: USB floppy drives do work... and I believe I have seen some BIOS feature which will allow you to emulate a floppy disk with a USB flash drive. Whether your board supports this or not, you'd have to investigate. To get these drivers, you can navigate to your motherboard in the support area, and you'll want to find this (under the "Drivers" section) -- RAID: Intel® Matrix Storage Manager Driver for Intel Desktop Boards. Once you click this, you'll see these up for download:
STOR_all32_f6flpy32_188.8.131.523_PV.zip - F6 driver diskette for Windows* 7 (32-bit editions), Windows* Vista* (32-bit editions), Windows XP* Home, Windows XP Professional or Windows XP Media Center Edition.
STOR_all64_f6flpy64_184.108.40.2063_PV.zip - F6 driver diskette for Windows 7 (64-bit editions), Windows Vista (64-bit editions) or Windows XP Professional 64-bit Edition.
You'll of course want to download the appropriate 32-bit or 64-bit version depending on the OS you are installing... unzip these files... there should be 5-6... such as iastor.sys, etc. These are the RAID drivers. Once you select this location to load the drivers from, you will be prompted to choose the chipset... it will be important to know this beforehand. Do a little research if you don't know... you'll see different versions such as ICH8, ICH9, ICH10 -- these are just revisions/versions of the chipsets. Seeing a "D" in there will usually mean "Desktop", "M" being "Mobile".
Actually, the documentation is quite clear, moreso than I could be...
please refer to this link: http://download.intel.com/support/chipsets/imsm/sb/8_x_raid_ahci_users_manual.pdf
It is a PDF document; I would read the whole document for your own clarity, but sections 3-5 address this issue in particular.. that is, 3-- tells how to enable the correct mode in the BIOS, 4-- talks about identifying the chipset used and other info and 5 -- talks about the F6 drivers and installation method.
One final note, while it is required that you install the drivers for an XP installation, Vista and Windows 7 will automatically install them, therefore it is not required for Vista or Win7 -- although it is still possible to select your own driver (and may be wise to download the latest version and tell it to use that driver). Thankfully, in Vista and Windows 7, USB thumb/flash drives are supported, making this a much simpler process without the floppy disk headache... just throw the drivers on your USB flash stick and select "Load driver" from the main installation screen, then point it to the correct location.
And finally, once the OS install completes, you must install the Windows software, called the Intel Matrix Storage Manager. This software runs mostly in the background and monitors the state of your RAID volumes, alerting you in the event of any degraded arrays (failed or missing drives, etc). It also provides an interface to view and interact with the RAID arrays through a GUI (Windows) interface. All of these instructions are in the above PDF file. Failing that link, just do a search on support.intel.com for "Intel Matrix Storage Manager" to find drivers and documentation.
Hope that can help clear the process up for anyone who may come across this thread in the future looking for help.