Alicia, I doubt a trainer will be able to help you on the rowing machine unless he's a rower. The instructional video is your best bet, provided you follow it carefully. I'm interested in who the instructor is on that video? My favorite coach of all time actually works for Concept II, and we visited him at the plant there in Vermont. Larry was the only coach who never needed a megaphone. In fact, they gave him one for Christmas one year, with a pillow stuffed in it!
If you decide to buy an ERG and want to hire a PT to come train you, I strongly recommend hiring a ROWER (ideally a coach) in your area. Call the closest rowing club and ask them.
" . . . it takes up less space, and is moveable." Actually, this is not true. Our ERG takes up the entire right side of the bonus room here over the garage. We designed this room around the machine! Although it can be moved and comes apart in two pieces, it is not easy to do; you would not want to do it every day. The treadmill we had took up FAR less space.
I am partial to the treadmill because it got me into shape faster than anything. However, when I had my knee surgery and all the cartilege removed, I could no longer jog, and even walking is very painful. Rowing was the most therapeutic exercise; thus, I use the ERG now instead of the treadmill.
If you do decide on a Concept II, you won't be sorry; it is the best on the market. In fact, I wouldn't even consider any other kind of rowing machine; they're all junk to a rower.
The monitor is an excellent coach; it gives you your output. You want to keep your stroke rate down to around 21-22, but you want your output to be in the 200 range if you can. It's not easy! The trick is to drive REAL hard with your legs, and then SLOW up the slide on the recovery. Also, do not pause before driving again; you don't want any time to lapse between strokes, which on the water transfers to the boat actually slowing down. Just be sure to keep your knees together, regardless of how large your tummy might be. Drive with your LEGS, not your back!
If you DO get an ERG, and you really get into rowing, you should order "The Rower's Companion," a video published by U.S. Rowing Assoc. that we use when we're in shape. They mounted a camera on the bow seat of an eight comprised of Olympic rowers, and they do three different workouts on the Charles River in Boston. You actually feel like you're in that boat with them, and you just follow them on the ERG. It's a FANTASTIC workout! You're sweating bullets before you realize it because you're having so much fun rowing with them.
I hope you do decide to get the Concept II, but more importantly, I hope you get some really good coaching on it. I have thrown out my back more times than I care to remember.