I’m no professional by any means but I’m pretty sure others will advise you to utilize a workflow that works best with the equipment you have. If you have a slower processor (I believe having a duo-core or other equivalent is adequate for video editing) and/or less ram it would be in your interest to transcode to an intermediate file using Mpeg Streamclip (Avid DNxHD codec in a .mov container) or using Cineform Neoscene. Each program has it’s advantages but Mpeg Streamclip is free and Cineform will run you at least $100. I hear others saying that the .mov container is still taxing for a PC and is better suited for Macs. I’ve also seen others claim that Prism video converter with the Matrox codec works better for Sony Vegas Pro and Windows OS. (Please note that these intermediate files from either option will create files between 2-4x larger than the original H.264 files!)
Your best bet is to go ahead and try to edit a short clip taken with your DSLR (assuming you have purchased it) and see how well your computer plays it in the preview window and the corresponding render time needed for length of clip (ie. 15 mins need to render for approx. 1 min of an edited clip). Some computers have the specs that handle the raw H.264 clips from Canon DSLR quite well, making intermediate files unnecessary. Either way, I advise that if you do use intermediate files to back up the ORIGINAL H.264 clips as you can always re-encode to intermediate files and it is more convenient to backup the original, smaller files.
Hope some of my rambling helped!
Josh