Hi rtpshopper !!
First, since you mentioned you're going to be 60 this month
I'm 55 and had my left knee replaced in '06 and the right in '08. The most important thing you need to know (IMO) is that the experience is very different for everyone. In fact, I was surprised when having my second knee done because it was nothing like the first.
Certainly, exercise and losing weight before your sugery would be a good thing. But, pain and fibro can make that seem pretty overwhelming! The exercises my surgeon had me focus on the most were the ones to build strength in my legs. Most of them can be done laying down. I just remember that although they were hard to do, they weren't really painful. And didn't aggravate my fibro.
The book Meg recommended is a good one. I used it before and after surgery.
Talk to your surgeon and explain very candidly what you can and can't do, given both your current knee pain and your fibromyalgia. Then, ask what's the best plan for you in terms of getting ready for your knee replacements.
The recovery wasn't easy for me, but I'm certainly glad I had it done.
(I haven't been here long enough to PM you, but feel free to contact me)