DPP is excellent raw processing software, and gives a result close to that of an in camera jpeg. Many people feel that it gives a better result with Canon files than LR does, which would make sense as Canon don't share their data so Adobe have to work backwards and take a few guesses. LR does have the advantage on highlight recovery - it can recover data from overexposed images that DPP doesn't even know exists.
That said, LR is a much more workflow friendly program. It will not only process your raw or jpeg files, but will also catalog them for easy reference, create slideshow, web galleries, print and so forth. It is also much simpler to copy settings from one image to another when processing, which makes it much quicker when dealing with a large number of images. DPP has no real cropping or retouching facilities, so you have to take images into another application, whereas LR has even built in light spot retouching facilities as well as straightening/cropping.
And finally, DPP is free, LR is not.
There are plenty more differences, but it sounds like you already have the DPP disc. Why not download LR's 30 day trial and see which suits you best?
Victoria
