Microsoft generally recommends that you use a Storage Area Network (SAN) or locally attached disk for the storage of your Microsoft SQL Server database files because this configuration optimizes SQL Server performance and reliability. By default, use of network database files (stored on a networked server or Network Attached Storage [NAS]) is not enabled for SQL Server.
However, you can configure SQL Server to store a database on a networked server or NAS storage server. Servers used for this purpose must meet SQL Server requirements for data write ordering and write-through guarantees, which are detailed in the "More Information" section.
http://support.microsoft.com/kb/304261