ok here is my take on the digital rebel vs the 10D, having handled both in a variety of conditions in and around a local camera shop, and editted the pictures. First off the technical pieces.
build: the build of the rebel is more plastic then metal build, even though the sub frame is metal, were as the 10D is a solid metal frame similar to the canon EOS 3.
internal electronics and sensor are the same for both.
metering: this is were the two cameras are really different because on the rebel its all automatic and chosen for you were on the 10D you have several styles to choose from or set it to focus only on one particular point. also the AF on the 300D is allitle bit more rough and clunkier then the 10D which is supposedly based of either the same AF as the EOS3 or Elan 7e.
flash on the the 300D is like most point and shots it sense what output it needs and sets it in the camera for when you take the picture, and will sync to a external flash to a max of 1/200 of a second. were as with the 10D you have up to a 1/500 and you can control the flash compensation on the onboard or external flash.
images and size: both cameras take the same and can take both jpegs and raw images(for those who want the ultimate control in post editting) but the difference in imaging is that hte 300D processes the images like any other P&S cam would do, were as the
lens mount the the 300D has a special lense mount called the EF-s mount which uses both normal EF series lenses or the new EF-s mount which lenses are designed for digitals only, which at this time there is only one lense and that the 19-55 lense that is sold with the 300D. one thing to be aware of is that both of these cams have a 1.6 crop factor as to using a normal camers so at 20mm on the lense mentioned above its actually 32 mm.
all the tech specs are good but you have to remeber that the digital rebels images are processed in the camera so that they will be sharp or similar output to most consumer and P&S cameras. With the 10D you will have to work on the images to get them to look just the way they will need to get the same results (ie some adjustment and sharping of them image). This can be done in PS elements or a full version of 7(as long as you have the RAW plugin to convert the image) or CS(new and just realeased
overall both cameras have the ups and downs, but i personally would get the 10D because i have more control over the process of how images are processed, and for low light the 10D is real good.
if you want a complete review take a look at one here
http://www.dpreview.com/reviews/canoneos300d/ 300D Digital Rebel
http://www.dpreview.com/reviews/canoneos10d/ 10D
Your Mileage May Vary
