You can't install it and apply striping. Go to the bios or (first, check the BIOS. Enable the raid controller, it can be disabled so just check it/enable it. And build up the raid if its possible from there if not, read on) simply the raid configuration setup (usually it comes right after the BIOS, watch out which hotkey brings it up). There config up your HDD to raid0 and there you go. Then install Win7 like you'd do, that's all. (Maybe you'll have to install the raid drivers after the first boot by ASRock, check the website. For me I have to with NForce raid controller.)
(NOTE: (Yeah I know you are tired of this): If one of the drives go dead, you'll lose every data of yours. Recovering from raid0 is possible but its really hard, you as a single user can't do it. A friend of mine's father lost his data due to a raid0 failure. An expert wrote an application for a cheap price (about 1100$) which recovered all of his data. Though, at a company I know (Kürt Kft.) you have to pay about 2233$ for a recovery like this.)
Checked ASRock's website, and yes there is a RAID driver available there. Selected Windows 7 and it threw it out but I guess you need this only for XP. (You know when it says "Press F8 to load..." when the installer is loading stuff.)
Anyway, here is the link. (The link leads you to 32bit Win7.) Here is the chooser.