I would avoid RAID as it is problematic with Windows 7. But you need to study your mobo manual to understand its settings. This thread is hot here right now: AHCI, can someone explain?
In the BIOS setup page accessed by tapping the F-key given on first BIOS screen, it should have a Boot Tab (read your manual to be sure) which allows you to set which device boots first, second, third, etc.
Set the DVD drive to boot first so you can boot your Windows 7 install DVD.
It will prompt you after startup to "Hit any key to boot from CD/DVD drive" which will boot the DVD.