Wow, there has been a lot of advice given in this thread. Sadly, my experience shows me that all of it is fairly useless. I think the original poster who asked the questions already had the best set up for his needs.
Having multiple drives for different OS's and for audio storage will certainly help a system run smoother. On the internet/gaming/non audio drive you could even set the OS up to not recognize the audio and the audio OS drive. This will reduce the chances of getting a virus, and other people screwing it up. I would even make that drive the default bootable for one added layer of protection. Multiple OS installs will certainly be less risky then constantly installing and uninstalling on one drive as well as make the 2 OS's much easier to setup appropriately for the different uses. It will also increase speed and throughput of the system.
As far as RAID goes. Someone above reccomended you set your system up with a striped raid array. I would HIGHLY recommend that you NOT set up a striped array. Modern hard drives are generally fast enough to handle much more than what people throw at them. On paper there are plenty of reaons why a striped raid array would be useful, but in real life there is one giant reason that in my opinion outweighs them all. Stability! First, the speed increase of your porgrams and recordings will be faster, but by a much smaller amount than what the paper specs would leave you to believe. However, if you lose a drive due to hardware failure (which is pretty inevitable in this day and age), than you will lose all of your data. Sometimes expensive hardware recovery is possible, but if that drive happens to be the "master" of the two striped drives than even that hardware recovery (which could easily cost hundreds) could be useless. If you are lookng into a mirrored array, thats a whole different story. A mirrored array increases your chances of NOT losing data
Sure they may be better ways of doing what you need Stu, but given your stated resources and goals, I think you already had the best way possible