Actually, your answer is not completely correct. in all likelihood you do not want to break the RAID.
First, if the system is under warranty, call HP. If it is close to still under warranty, I would call and see if they will cut you a break. Make sure to tell them that you are actually using the hardware RAID.
1/ Get a replacement drive. If the system is under warranty, HP should send one. If not, go buy one or order one online. The replacement should be the same disk if at all possible. If not, it needs to the the same size or bigger.
2/ If you haven't already, take a backup. At the very least, get a Dropbox or SugarSync account and get a copy of your important stuff off the machine.
3/ If you don't have one, create a Recovery Disk. The specific procedure depends on your OS.
4/ If you haven't already, figure out specifically which drive has failed. The error codes might make it clear, or the raid array management utility might tell you.
5/ I presume it is not a hot-swappable RAID controller. So, turn off the system, swap the failed drive for the new drive, and start the system. Go into whichever tool you used to create the RAID set, and confirm that it sees the new drive and is rebuilding.
I would not reuse the bad drive in any production system. You could run SpinRite on it and possibly resolve the issue and keep it around a cold spare, but I wouldn't.
Best Answer
S.M.A.R.T. can be used as an indicator that there are drive problems but can never be relied upon to indicate that a drive is good. When there is disagreement between multiple diagnostic systems always favour the one that shows the worst results.