We ignore the BMI information. It's not the fault of the Wii, it's the fault of the various interntional health groups that have decreed what is a healthy BMI and what is not. I've frankly had a gutful of doctors and nutritionists over the yers telling me I'm an unhealthy weight when I'm not. I was told in the past that I was overweight at 65 Kg, when stats these days declare that to be a healthy weight. And after difficult child 3 was born and I weighed less than I do now (and the BMI now puts me in the overweight category) a doctor labelled me as "morbidly obese" when according to currrent stats, I was maybe just into the overweight range, but I HAD just had a baby!
So ignore the BMI as an absolute reference, just use the weight measures relatively, to monitor your body's changes. The Wii Fit Plus has modified its standards too, so there seems to be less pressure re BMI.
We're just getting into the Wii Fit Plus, my physiotherapist has warned me off some of the exercises, especially ones involving lifting my legs at all, but the new balance games are fun. I love the tilt table.
Enjoy it, Linda - it will do you good. Just be careful to not overdo it.
Marg