In icon view you can't do it with the mouse, but if you select an item and hold Shift, then use the arrow keys you can select a list of items that way.
20. Use Image Capture to get images from a digital camera, scanner, etc.
23. You can create another account with limited access to things. Look in Accounts preferences. I think Leopard is going to actually have an option for an account called "Guest" specifically for that purpose, dunno how that will be setup though.
24. From the Desktop, right-click, select "Change Desktop Background..." then you can drag and drop your image into the window. You could also probably setup an Automator action that would do it on one step (right-click on file, Automator -> Set as Wallpaper or something like that).