There are two ways to install the operating system in a system running RAID with Intel(R) Rapid Storage Technology.
One is the regular configuration, in which you enable RAID in the system BIOS (check with you motherboard or Original Equipment Manufacturer directly for information to do this since this changes from manufacturer to manufacturer). Then boot to the Control I Option ROM and configure the RAID volume that you would like to use (options may vary from manufacturer to manufacturer too).
Then proceed and install the operating system as normal, before selecting the volume and creating the partitions to be used, you should load the third party mass storage drivers, also known as F6 drivers when the operating system gives you the option to load those drivers (the option and time to load them would differ depending on the operating system used too, in Microsoft* Windows* XP you need to press F6 when prompted, in Microsoft* Windows* 7 you use the button that says "Load driver"). Once the driver is loaded, the operating system will continue installing as normal. Once the operating system is installed, install the version of Intel(R) Rapid Storage Technology that is provided by your computer manufacturer.
The other way to load the operating system, is with the RAID ready configuration. It is basically the same as the first one, with the exception that you do not need to boot to the Control I option ROM and create the RAID volume there. You will create the RAID once the operating system is installed and Intel(R) Rapid Storage Technology is installed in it. Then you enter Intel(R) Rapid Storage Technology control panel and migrate to a RAID volume from there.