My video camera shoots in HD. Sort of. It's a Sony camcorder with a built-in 60GB hard drive that stores what it shoots in AVCHD.
AVCHD is a very powerful compression scheme part of the MPEG 4 family of codecs. It's variation codename is H.264 and is what is used in modern digital broadcast TV in some places in the world. What it means for us, underwater videographers is that we need a hell of a lot of processing power to edit natively in HD because each frames needs to be decompressed and PCs (or Macs) are not super good at it. Plus these frames are huge: DVD format (or SD = simple definition, or D1), has resolution of 720 by 480 pixels. In comparison, HD has 1920x1080, that's 6 times the number of pixels. To make things worse, frame rates are also doubled with around 30fps for D1 and 60fps for 1080p... "Fortunately" my Sony shoots in 1080i which means I have "only" 30fps of HD...

So in order to be able to edit in HD in your little digital darkroom, you need some serious power. A quad core CPU with a decent clock speed is the bare minimum. Heaps of memory too and a quick and spacious hard drive. If you can throw on top of that a video card with some serious pipelined processing acceleration (CUDA for Nvidia and FireStream for ATI), that'll add some heavy lifting capability to your rig. But still, don't be surprised if what used to take a few minutes to render, now takes hours...