I'm guessing that you're trying to use the USB cable to directly attach the camera to the computer....
Do you have a memory card reader... either built in to your computer or an accessory one? If so, it's usually better to remove the memory card from the camera, insert it into the card reader and download from that. The card in the card reader should "appear" on your computer as an additonal removeable drive.
The download can be automated with various software.... but also can simply be drag & drop copying of the images from the card to some folder you've set up for the images on you computer.
If I recall correctly, the 300D uses Compact Flash memory cards. Just be a little careful with those, removing and especially inserting them into the camera and the card reader. CF card sockets have about 40 little connecting "pins" that insert into corresponding holes in the end of the memory card itself. Never "force" a card into the socket. Those pins can be bent or broken if the card is misaligned.
Personally I've switched CF memory cards out hundreds or maybe even thousands of times and never had a problem. But I've seen cards and card sockets damaged by careless use.
Also, what software are you using? EOS 300D is a rather old Canon model that probably isn't supported in more recent Canon software. (I know that's the case with my 10D, which is about the same age as the 300D).
Third party software such Elements, Lightroom etc. can handle the older image files just fine. The drag, drop & copy method mentioned above should download things just fine, too. But if you want to use Canon software, you might not be able to use the latest and greatest available from their website, may need to track down an old version that supported the ealier cameras.
***********
Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7DII (x2), 7D(x2) some other cameras, various lenses & accessories
FLICKR & EXPOSUREMANAGER
