Canon EOS 20D Digital zoom failed

Hi there,
The autofocus mechanism on some lenses can be damaged if you manually focus while the camera is attempting to autofocus. Basically, you would be working against the motor and gears. 
There is no need to download software before using the camera, however, I would suggest going to Canon's website and downloading the firmware upgrades for it. Here's the link:
Canon 20D Firmware Download
Hope this helps!