^^^^^ what stephtu said X2.
Something like this would be a great starter bike, as long as the fit was good.
http://dallas.craigslist.org/dal/bik/4270677910.html
an old rigid mtb is great for heavier beginners. suspension on a cheap bike is really a waste, from a weight and usefulness perspective.
if you're going to stick to the roads, don't shy away from something like this either:
http://dallas.craigslist.org/dal/bik/4271345772.html
although, on that one, the price is rather low it seems, at least I hope it's low as I have a similar bike that I'd like to get 300 for this spring. Read into that what you like.
Don't worry so much about your weight. At 250 I started riding my carbon road bike with relatively low spoke count wheels. 6500 miles later and no real problems to speak of. couple broken spokes, but that could have been the cheap wheelset I was using. I"ve really put some hard miles on that bike. My favorite was hitting some broken pavement on a downhill at 30 mph. I had to stop and convince myself I hadn't destroyed my wheels.
Youtube is a great resource for DIY bike mechanic info. You don't have to be particularly handy to work on a bike.
Also, assuming you have small children, skimp on their bikes and spend more on yours. As long as theirs are fairly functional, they will ride. Plus they'll be outgrown soon enough.
DFW area may have a bike co-op. There were a couple old threads on here where people wanted to start one. That may be something to look into as well.
Good luck on finding some bikes and your future weight loss.