Document Management Solution

Hello, I require a document management solution with the following characteristics/requirements: - Multi-user - All users access the same share folder - Individual access code or group access. - Capability to read, write, edit files from server location without having to save first on local drive and then upload. (similar to sharepoint or webdav functionality). - Ability to Lock (Check out/in) files to avoid other users to modify the same file a user is working on. - It should work in my current server environment. Server environment: - Web server with Linux Centos - Dedicated Server, but this solution should work on a shared hosting account. PHP5 running on mod_php (possibility to upgrade to cgi if necessary) - Apache 1.3 (possibility to upgrade if necessary) - MySql 4 (possibility to upgrade if necessary) - cPanel 11 (currently cPanel webdisk is enabled and working. Apache/mod_dav is NOT loaded). Client environment: - Windows Vista and XP. Note: I have tried webdav clients ([login to view URL] webdrive, netdrive, etc) with my cPanel webdrive (webdav) with no success as I can not get the file locking to work. I'm open to try again this approach if you have a work around. Bids should detail your solution approach. Also, I would prefer bids that have some kind of demo to try out and see all requirements work. Thanks.