If you're looking to put ALL of that gear in one carry-on, I think you might be overly ambitious.
BUT here's what I do...
I have only one housed camera which I carry in a wheeled backpack. This was a standard nylon off-the-shelf, bought-it-at-Mervyn's kind of no-name backpack which had wheels and a handle. It holds my Olympus 5060, Light and Motion Tetra Housing, two Ike DS50 strobes, tray, and arms, and has held up pretty well for better than 2 years. I pack my gear inside the bag with bubble wrap and t-shirts. Who needs a pelican case and their crazy foam?
This bag ALSO holds some toiletries, portable hard drive I use to copy off images, battery chargers, iPod, passports and a book or two. I currently do NOT take my laptop with me on dive trips, as I just copy off the pics when I fill the memory card and edit when I get back home. If I feel like previewing I do so from the camera on a TV monitor or on my portable hard drive's LCD viewer and make my notes to myself for corrections or what have you.
In your case, since you have two housings and a laptop, I'd go with a roller bag like the Samsonite and a separate bag for the laptop (standard laptop bag, or even a laptop backpack). Both perfectly legal as carry-ons, which is what I usually travel with on non-dive trips. I know a lot of people are big on Pelican cases because of the foam cutouts and waterproof seal, but geez those things are heavy and usually no wheels. Plus, seriously, how often are you going to need that watertight seal? For me, and I actually HAVE a Pelican case, too, usually the case stays in the room and only your rig goes on the boat. Anyway, the Samsonite Pro-DLX carry-on will fit in the overhead, fit both your housing and camera gear, and it's a nice bag to boot which you could use for other travel needs:
Amazon.com: Samsonite® Pro-DLX Carry-On Upright: Apparel
$220 at Amazon. Pricey, but it's a Samsonite. You could probably shop and get a better deal on something similar. Anyway here's what it looks like:
That suit holder thing comes out and you can toss it to make room for your gear, and there should be room left over for other stuff. Putting more stuff in the carry-on will help you keep your dive bag lighter and avoid the extra charges they stick you with on these 50lb weight restrictions.
Clearly the above is just my take on a possible solution, but I hope it helped!
