Check out Assembla:
http://www.assembla.com
FAQ page here:
http://www.assembla.com/wiki/show/breakoutdocs/FAQ
We're just starting out with it, so I can't totally vouch for it, but it looks promising. It's totally free for small groups!
Also, not sure if it requires anything other than port 80, but it is all web-based, so you might be okay.
Oh - and you can make your space totally private, if you so desire (or if you're using Kevin's code
)