A – STAY AWAY FROM WEBDAV! It was intended for quick changes to webpages and subject to many vulnerabilities.
1 – If you have Windows Server 2003 and the hard drive space the ‘Volume Shadow Copies’ is first step. Automatic backup (timed) for folders, allows client recovery of previous version if you install client on 2k pro client is already in XP.
2 – Share Point Services/Portal – on a 2k3 server with big hard drive setup services and put your document libraries(folders) under ‘SharePoint’. This has Document checkout / checkin, multiple user tracking, and change resolution. If you are using Office 2k3 with infopath it can almost transparent to the end users.
3 – There are several ‘open source’ CVS (content version system) choices and dozens of commercial packages if you want the 3rd party support. The biggest variable is the amount of retraining required for the end user. If they are used to everybody having their ‘own’ copy of a document and round robin editing fights, then they may resist change.