I bet you miss all the attention!
SidC - you asked about a rowing machine? That is such a complex question!
Let me state my goals, and then try to break down some possible answers to your question:
My goal is to look muscular and lower my bodyfat%, and then move into some high-intensity training for my cardiovascular system, so that my heart will be buff as well.
For the time and effort, I (me, myself, yours truly) am not going to do aerobic exercise, because I don't think that it is a good investment of my time, and the results that aerobic exercise gives you - I do not want (lean, efficient muscles). I believe aerobics burns calories while you are doing it, and resistance training builds muscle, which burns calories all the time. Now there is no question that aerobics is superior for your cardiovascular system, and burns fat off your body - I would never try to dispute that.
Now, rowing is an aerobic exercise - unless you are puposely trying to do high-intensity (like sprinting) - it will work the legs, arms, and back, and make those muscles (and your cardiovascular system) leaner and more efficient. This will mostly burn energy while you are doing it, and afterwards for a short time.
Similar in motion, rowing with weights will work the back and arms, and make those muscles larger (much larger for men), and less efficient. This will cause the muscles to grow, the exercise will burn energy while you are doing it, and larger, more inneficient muscles will burn energy around the clock. Unfortunately, this does not do much for your cardiovascular system.
To sum it up:
Resistance exercise will help you shape your body and burn lots of energy all the time, but will not help your cardiovascular system.
Aerobic exercise will burn energy while you do it and greatly benefit your cardiovascular system, but it's not that great at shaping.
Having said all that, what are your goals? Do you think you might need one, both?
The best answer I've seen with the aerobic michine questions is: "Get whatever you'll enjoy and use all the time." If you will hate it, don't waste your money!