Manual focus is best for accuracy on macro photography, but since you want to know about auto-focusing, here it goes:
1. Turn the AF/M switch on the lens to AF (this is very important)
2. Activate auto-focus using "C. Fn. III-06 AF During Live View Shooting. Choose to "anable" this feature (in the Menu)
3. Press the AF-DRIVE button and use the Main Dial to make sure the auto-focus mode has been set to One-Shot (on the LCD screen)
Thanks but we're not using Live View for macro photography, and not sure that we would use it for that though I guess it would come in handy. At the time we dug around in the CF menu's and figured out what had to be done.
I own a 30D and a 5D, it was my brother who bought the 40D.
After playing with his 40D for a day, I could almost buy one .... give my 30D away, and the 5D would see less use.
This 40D is impressive, and putting live-view in it is a big plus.