looking to start biking

I am suprised that no one has responded. As you are heavy, look for a heavier than average bike. Look for a higher than average spoke count (at least 36, but 40 would be better). Check out shops that carry tandem bikes. You don't need a tandem, but the components carry two riders. At 6'9" you would dwarf me. Look for a llllarge frame. Don't consider anything less than a 60, and larger will likely fit you better. Get a steel frame, consider a mountain bike or a hybrid. At 400 lbs, a few extra pounds of bike frame will not mean much. Make a friend at a decent LBS (bike shop) and see what they have to offer. Test ride to see what fits and feels comfortable. Everyone is different.

Consider a touring bike, like the Trek 520. They generally have heavy-duty steel frames and extremely strong wheels, as they are meant to carry the rider plus a full load of camping equipment. They are heavy compared to most road bikes, but as Butch said, at this point you should not care what the bike weighs.

I am only 6'0" and was comparatively svelt at 265 pounds last fall. My 2004 Specialized Crossroads Elite has no problems with my weight, and might well stand up to your weight, but the Trek 520 might be a better option for you. I am now down to 208 pounds, so I figure I have already lost as much as two bicycles weigh. Loosing the weight was better both physically and financially for me than shelling out five or six times the money to get a lighter bike. When I hit 180 pounds, I plan to get a real road bike.