Windows 7 will boot from a RAID5 array. You need to set the array up before installing Windows. I think that Win7 is smart enough to have the RAID drivers available by default (I have not tested this). If not, you will have to download them to a thumb drive and use F6 to add them to the installation process.
My usual question: What do you intend to accomplish by doing this? If it doesn't address a specific need, and you are not doing it just for fun, I usually recommend against using RAID.
Most mobos cannot boot from volumes larger than 2.2 TB, so watch your volume size. And remember, RAID is not a substitute for backups. Do backups too.