Download the RAID drivers from the Intel website, extract them to a USB thumb drive and use the F6 install method. Windows 7 (unlike XP) will allow you to 'browse' to the USB drive to find the drivers.
You can use the Windows 7 drivers supplied by Microsoft ( on the Win 7 setup disk) for a Raid / AHCI install. You could ever since the Win 7 beta. Also you can load any third party drivers onto a cd or a usb drive and browse to them during setup. Installing the latest Intel Raid driver afterwards is ok to get the Trim function for ssd's. ( Altho, the M'soft driver supports trim also)
Remember, you need to set up Raid volumes via Ctrl+I during bios boot. Before you start Windows 7 Setup. And the Raid option needs to be enabled in the bios.