The rowing machine is one of my favorite machines that I use at the gym. It is great for the whole body and I was told once that doing 15 min on the rowing machine is the same as doing 30 min on the treadmill ( not sure if this is true or not) . My back has never bothered me doing the rowing machine. Did you have someone show you , how to do it the proper way?
I alternate between the rowing machine, treadmill and elliptical trainer....that way dont get bored doing the same thing.
Hope this was of some help.