Hi Rainess,
Unfortunately what you are proposing is very tricky to do for several reasons. If you do a search through the forum posts on RAIDO you will find several which have met with very little success - if you search back far enough, you will even find my original post about exactly what you are proposing. The fact is that installing an OS to a RAID0 just doesn't seem to be very succesful.
In theory you could image your existing setup using something like Macrium Reflect, then install your 2nd hard disk, configure the RAID controller, then restore your image back to the new RAID0. Unfortuantely, however, you are going to run into problems : one of them that I am aware of is that the REGISTRY will require a reference to the fact that your system is now a RAID, but your image you are restoring doesn't have that reference. There is probably some registry fix/hack for that, but I have never attempted it - I have seen others try it with very limited success.
A more robust solution is do a clean install of everything onto the new RAID, but even that doesn't seem very successful for most - I really don't know why. For this reason, many people here will advise you against using a RAID as an installation disk. Of course, a RAID0 is also a risky undertaking, since if a single disk should fail, then the entire RAID fails - you will lose everything on those disks.
Since you are looking for speed increase, and if you can afford it, I recommend considering a SSD as your OS disk, with the other disks as data/backup disks. This is the tried and tested solution that has worked for many here, and an SSD far outperforms any RAID0 I have worked with, and I have worked with some very quick RAID0 arrays.
Let us know what you decide.
Good luck,
Golden