Well, The other similarity between rowing and cycling is that they are both sports you do sitting down.....

Regarding back problems; I have rowed for over 10 years now (several of which at elite level) and have never had a problem. However, I was lucky to have some good coaches who spent a lot of time telling me to sit up straight. The key seems to be to make sure your back and stomach muscles are strong and then remember to use them while you are rowing. Often back injuries result from trying to pull hard with poor technique.

For technique while using a rowing machine, the conceptII website http://www.concept2.com/05/default.asp has some tips.
Try: http://www.concept2.com/05/rower/rower_alex_anim.html

http://www.concept2.com/05/training/...ingstarted.asp

The last link even has an address to send off for a free technique DVD.

One thing that I think of when training at lower intensities is to breathe in time with my rowing, so that as I push off with my legs, I start breathing out, at the same time using my stomach and back muscles to keep me sitting up straight.

I hope this helps.
Bron