well im happy you chose a camera id relay like to hear how it goes (pm me if you want).
the T3I (aka 600D in the uk, i like the uk names
) is a fine camera, get used to manual focus (fixed unless you have golden hands for focus pulling) and think about getting a nice lens if you can, depending on what you need the basic 18-55 is lens is a tad soft and slow.
IS is vary nice but will be picked up on the internal mic
think about custom image styles i use Flaat_10 most the time,
http://www.similaar.com/foto/flaat-picture-styles/
comparison video
http://vimeo.com/46037571
you will need something like mpeg streamclip
http://www.squared5.com/ to convert your H264 files to prores (or other codec)
id recommend manual video exposure but thats up to you, at least use the exposure lock so it's not bouncing around all over the place and get the WB correct as it's vary compressed video your capturing there's not much latitude in post (both WB & exposure).
dont know where you live but if it's hot & you shoot outside you may need a shade for the T3i to keep the sun off or it may overheat.
the one big problem with Dslr's and video is there just not a good shape (and weight distribution) for handheld shooting, so just dont try unless you want your video to bounce round more than a bouncy thing, nothing says neat like a tripod shot video (or mono pod)