SDLC,
Yes you can create a new array without causing any issues with the primary array. The Perc 6/i can support multiple arrays, up to 64 to be precise. You may also use different specs on the drives as the first as well, but all the drives in that array must be the same or larger. Meaning, you can have you 4 15k drives in the 1st array and then have a second array created with 10k drives, BUT all the drives in that array must be 10k or higher.
Quick question, are you using Open Manage Server Administrator with the host?
If not, then you will have to down the server to access the raid controller BIOS.
If you want to install it then you still have to down the server, but it makes it where you won't have to down it in the future to perform similar tasks. Let me know if you are interested and I can post the instructions.