Is this a bad thing to do? (Unix permissions)

As part of my new site I have created a php-driven guestbook. The guestbook entries are stored in a file called guestbook.txt. I found that in order to get the script to write to the file, I had to set the directory permissions for the guestbook directory and the guestbook.txt file to -rw-rw-rw- ... is that a bad thing to do? Does it expose me to any hacking problems? If so, what should I have done? Bear in mind I'm using a 3rd-party host and I work in Windows, so please don't blind me with science ;) Thanks, Gwydion