Data availability can be achieved through…
…hardware redundancy e.g. RAID, multiple power supplies which connect to different power feeds which are protected by different UPSs. Network redundancy should be configured too e.g. multiple network cards (possibly teamed) to different switches (think you need 802.3ad / 802.1ax support).
…server redundancy e.g. using DFS, application replication e.g. Microsoft SQL server database mirroring or failover clustering.
…site redundancy e.g. redundant connectivity links or maybe DFS namespace configuration with replication.
Data availability through shared resources using DFS namespaces and DFS replication; more here
Another way to share and collaborate would be using SharePoint; SharePoint 2010 foundation is available as part of Windows Server 2008 R2 licence.
Offline data access
Data availability through offline files; more here