RE: Rowing machine and Interval
You can use the same methods as any other form of exercise. The only point to make is that the benefits accrued from rowing don't necessarily transfer wholly to other forms of exercise other than a general increase in fitness levels. i.e. a fit, fast rower may not be much cop at running.
That said, interval training can be very effective done on a rowing machine and the ultimate goal could be to see how you measure up in the 2K challenge on the concept2 rowing machine. This is a longish sprint, which towards the final stages, pushes you close to passing out with oxygen debt. You can go onto the concept2 website to see how you match up to the worlds best. Definately one for the masochist. I got 6:37.4 mins on my one and only attempt last year which placed me just outside the top 300 all-comers in the UK last year, not bad for a clapped out 39 year old. And that is without having any formal training. I don't think that a lack of technique in the strictest sense of the word should hinder health benefits overmuch, the rower is a very forgiving machine in terms of injury etc.
Longer distances are ok, but I find myself lapsing into a bordom induced coma at anything over 18 minutes.