Quick Read/Write/Execute Question

Okay. Basically, I’m a baby who’s afraid of new, harder things. Instead, I try to manipulate what I already have. Basically, this is what I am trying to do:

[list]
[]Have an XML file that holds user data
[
]Have this accessible by my PHP and Flash programs
[*]Have this unaccessible by viewers
[/list] Is this possible? If so, what would I set the permissions to?

Thank you.