I would install the 2TB HDD in another computer, download and use TestDisk
on that computer to try to recover/restore the Master Boot Record (MBR), and then recover the files that still exist. Then, in the BIOS, "break" the RAID volume on the original computer. Create the new RAID 0 volume on the original computer using the BIOS to set the 2 150GB HDDs into the new volume. Install your operating system. Then re-install the 2TB HDD to the original computer.
Be sure to read the TestDisk wiki and understand what it will do. It has examples for recovering data in Windows systems. I have used it successfully several times. It is free and is not crippled - it will find and restore the MBR if it has not been overwritten. It will find and restore all your files - again, if they have not already be over-written.
When I setup a new system I only install the drive(s) for the operating system. After I install the OS, apply updates, and see that it is working well - then I install other drives that I want to use for storage - not criticism, just a tip.