The camera is a 1Ds MkIII.
I am new to photography above or beneath water.
Woah, you sure are jumping in with both feet. That's Canon's top of the line body - I'd love to have one of those myself. I think, though, you may be setting yourself up for failure by starting into underwater photography without a thorough understanding of photography in general. Unlike land photography, you pretty much have to go to manual exposure to get good results, so if you're still fuzzy about shutter speed, f//stops, how exposure works, and particularly how distance affects flash photography, you may find yourself underwater with no real idea how to correct the problems you're having.
Of course, you really have to photograph what interests you. And if UW photos are the only thing that motivate you to use the camera, I guess that's where you have to start. I just don't want you to get frustrated before you find out how fascinating UW photography really is.
Personally, for a full-frame camera like the 1Ds III, I'd equip a EF 17-40 f/4L lens for wide angle shots. I don't like the distortion of a fisheye, and 17mm full-frame is very wide indeed. I dove with a lens that has a 16-35mm equivalent field of view, and I ended up using 35mm almost all the time in Hawaii. Of course, if you like the distortion, by all means use a fisheye.
However, as I said before, I found the macro lens far, far more useful in Hawaii, and the Canon 100mm macro that you own is an excellent lens.
Just in case you haven't heard this before, you really should have a flat port (underwater lens housing) for the macro lens, and a 8" dome for the wide angle. Since you're completely new to this, you might want to consider diving with just one of the lenses, and leave off changing lenses between dives until you're more comfortable with the equipment. Not that changing lenses is at all difficult, but you need to be particularly careful not to say, drip seawater into your body, and it's one more complication while you're still learning the basics.
Yes, the 10-17 is not designed for a full frame, so someone gave you some bad advice on that one.
My immediate thought was "how did he manage to mount a crop sensor lens on a full frame body?", but sure enough, reading the Fred Miranda forums indicated this lens has a EF instead of an EF-S mount, even though it's a crop sensor lens. Maybe they intended it for use with the 1D, which has a 1.3x crop? The very first review says the vignetting isn't a problem at 14mm or longer.
So in effect he has a 14-17mm fisheye... which isn't terrible, though some of the reviews mentioned strong chromatic abberation.