when you create the RAID it will destroy all data and then you will have to reload the OS. RAID 0 is not really worth it for end users at all, unless you deal with large amounts of data throughput, ie you are editing and using multiple files that are all many gigabytes in size. Like editing video, or encoding or perhaps even rendering you may see performance increases.
DVD play back, video games, web surfing, office productivity applications, and so forth will not benefit from RAID 0. Furthermore, if one drive goes south the whole RAID array fails and your data goes out with it.
I suggest you reconsider running RAID 0, and if you must at least look into running a RAID 0+1, which would require 4 HDs, but then at least you will have a mirrored set of your RAID 0 in case it crashes.
If you run windows it will crash too, I have never seen a RAID zero run for years with out issues on a Windows box.