On Windows Server 2003 there's File Replication Service (or I think it's Distributed File System...can't remember). Either way, this feature allows you to create a file system on two separate servers and then let the service replicate changes from one side to the other. It's been a while since I read about it or touched it so I can't give you any more details.
Killable is correct DFS is also on 2008 but it's a newer version and its better. Know this your domain level must be at 2008 to use the NEW DFS. If your domain schema isn't there yet its worth the work. The new version has some decent enhancements that will make things more efficient.
( EDIT Oops I take that back your domain level must be at 2003 r2)
2008 Standard can use DFS with up to 1 other server. If you have multiple servers that will be performing DFS or replications to multi servers to one spot to need Enterprise 2008 at the "hub" at the very least.
File Replication Service is a Microsoft Windows Server service for distributing shared files and Group Policy Objects. File Replication Service can replicate content between Windows 2000-based servers that host the same fault-tolerant distributed file system (Dfs) roots or child node replicas.