User profiles and sharing programs

I've just trashed my old windows machine and went back to the Mac. So far I love it!
Got a few questions: With two user profiles. how do I share the programs that I download with the other profile? and secondly, can I change the avatar on my hard drive without changing it on the other profile?

Remember I'm new to the Tiger.
Later

If you put the program in the main Applications folder it will be accessible to anyone. If you place it in the Applications folder in your Home directory it will only show up for you.