I dont know how well this would work over the internet but i remeber reading a review on webmonkey.com about Macromedia Contribute which i think is for use like on LAN's for users to share their work and develope together and it has alot of features that your looking for.
Here is the official site:
http://www.macromedia.com/software/contribute/
Here is the webmonkey review:
http://hotwired.lycos.com/webmonkey/...l?tw=authoring
This is meant more for images and HTML files i think which could help somewhat. But i have no idea on how to do it for inventor files. We actualy had some sharing and revision problesm with the whole team working on inventor this year, eventualy we just had to assign people to be incharge of some of the bigger more complex assemblies...and you had to ask around before you made a change to make sure nobody was using it.