Well, given those, I’d recommend MediaWiki. It’s easy to setup, and folks are familiar with its functionality since it’s the engine under Wikipedia. http://www.mediawiki.org/wiki/MediaWiki
As for links to a filesystem, I think the biggest hurdle in an ad-hoc setup is consistent syntax, and local vs. remote filesharing. If you are all using Windows and are all local (or VPN//RDC connected to the same local network) then you just need a shared volume that you all map to the same drive letter, like X: Then links in the wiki can just be X:/servershare/directory/filename.xxx. There’s a similar AFP syntax for Mac users.
I’m less help with remote scenarios. I’m sure others here have more info there.