A typical raid 1 setup is just having two( or more) hard drives mirroring themselves (making exact copy) for backup or redundancy purposes. In this case it was to your benefit - imagine if you only had one drive with all your data and it failed!
So...
You should be able to replace the failed drive with a new unit and then use the raid manager to rebuild the array. You will most likely have to dive into the hardware settings to get the serial number of the bad drive and then pull and replace it. From my understanding though of raid arrays - (this is from a long time ago) you will want to replace the bad unit with a unit of the same specifications - RPM speed etc..
Alternatively, you could remove the Raid 1 array and rely solely on the good unit. (This isn't the case with other Raid setups) Obviously you would be down a 1TB drive - but you weren't really using it for space to begin with in a Raid 1 config - it was just backup.
This would be a no cost up front solution and could be done through raid manager.
Now what I would do is throw that windows computer away and get a Mac. Of course my opinion :)
