I have a new computer from HP that has Windows Vista Home Premium 64 bit
installed. Mostly, it seems pretty good. It has been quite stable since
initial trouble got ironed out (blue-screened severely, fresh out of the box
from day one).

Here's my current problem...

My daughter came to visit over the holidays and brought her laptop with her.
When she connected to my wireless network connection, her Windows Media
Player popped up a message saying it found [computer name] and did she want
to have access to media on that computer. She answered "yes" and proceeded to
show me that she could see all my pictures and movies, and play my music.

Doing some experimenting, we opened Explorer and clicked on the Network
line, and saw icons there for all the computers on this little home network.
We opened one of the remote machines and discovered that we can read AND
WRITE files to it, and can delete them as well.

This seems like a severe security hole to me - if I am mistaken, please
explain.

How can I prevent these computers from being accessible to each other on the
network?

Thanks in advance for any help you can offer.