I am looking for a good solution to collaborate on Microsoft Office documents, we currently just edit directly on a Samba share but it's one big mess because sometimes people leave the office with their laptops while docs are open so swap files remain there and then you nobody is sure what's going on.
Is there any good and simple open source solution based on Linux? I've tried Alfresco but it is much more than what I need, we got an internal wiki for most collaboration and I just need some solution for the stuff we need to do in Microsoft Office (mostly Excel files, the rest is in the wiki)

EDIT: Some more info as requested - we are very small group, 4 full time employees and a few freelancers.

The best idea I've got so far is just managing it in a subversion repository with a Lock-Modify-Lock policy but I'd love to hear about better solutions.

Thanks!