I love these photos, I wish any of them were 1920x1200. Need more backgrounds.
I googled hi res HDR backgrounds awhile back and found some pretty nice ones, maybe give that a shot.
As for the 1 shot vs 3 shot issue, 3 shots with different bracketed exposures is indeed better because you have three different raw images with full data to sample from. However, if you only have one raw image you can make what is called a pseudo HDR with the Photoshop Raw image plugin. Just load up the image, change the exposure down two stops, up two stops, and then save all three images and load those into Photomatix.
Also, a tripod is pretty essential if you are doing bracketing, however you can also just set your camera down on a solid surface if you don't have one. A shutter release shouldn't be needed unless you have Parkisons or something or are really picky.
ah the 5D Mark II... my dream camera.