RAID is finicky - if the drives have changed ports on the mother board, you will probably have to re-initialize the RAID array in your BIOS (even though it is recognized as a single volume). Unless you absolutely have to have a single volume, I would recommend changing it to Non-RAID, and create two volumes. If one of the two drives fail, you lose both.
In Windows 7, you can setup the Libraries to use the two volumes by going to your library, right clicking on the specific library (documents, music, pictures, videos), and putting a path to the folder. By default, these are set to C:\USERS\%USERNAME%\%Library%\. If you replace the C:\ with D:\ (assuming the drive letter is D:), the library will be moved to that disk. You can also have multiple folders - i.e. D:\USERS\%USERNAME%\%LIBRARY% and E:\USERS\%USERNAME%\%LIBRARY%.