Software RAID is RAID handled by drivers in the OS. By definition, when you're installing a new OS onto disks configured with software RAID the new OS is going to see the disks as "disks", rather than as a RAID volume. (A hardware RAID controller abstracts the disks in the RAID volume away and shows the OS a generic "disk".)
If you're installing the same OS, it should "detect" the existing software RAID configuration and use it. That will vary from OS to OS.
Finding official Microsoft documentation on this is proving needlessly difficult. From what I'm finding, Windows 7 Professional, Enterprise, and Ultimate support software RAID 0 and RAID 1. My experience with prior versions of Windows client OSs was that no software RAID was permitted.