First, you do have lifetime phone support with that system, they just will not send the drive if needs be. But they will walk you through some troubleshooting steps and also get a Dell part number for a hard drive if you wanted and then they couuld transfer you to thier spare parts dept.
Second, if you are going to replace the drive, you have to verify that the drive you are going to put in there is the same size or larger (most important) and same speed or faster. IF you found a drive like that then all you need to do is pull the failed on and put in the new one and it should start a rebuild.
However it is a good idea to get a controller log and see why the drive failed. Sometimes the failed drive is not the problem drive.