What kind of a server is it? Presumably you're using Apache. If you have PHP and MySQL Database Server set up, you can use phpbb. It's a free discussion forum, used widely, with plenty of themes available for download from their site. It's also fairly easy to revise a theme to your liking, if you take a look at their documentation.
LQ.org is running on a (much hacked) VBulletin. This one is also very, very popular and PHP/MySQL-based, but it's not free.
Then again, this may be overkill for 7 users. I don't know of any smaller forum apps, though.