Although not likely in technical conformance with the fine print of the accomanying license, Hyper-V Server 2008 R2 (and soon Hyper-V Server 2012), available for free from Microsoft, can install on a non-virtualization-capable computer and act as a non-GUI file server for a small home/business network. Using the “old school” command-line NET tools (e.g., NET SHARE), it is possible to create file shares on a Hyper-V server and make those files available in both a domain and workgroup environment.

You can download Hyper-V Server 2008 R2 and the Release Candidate of Hyper-V Server 2012 from http://www.microsoft.com/en-us/server-cloud/hyper-v-server/default.aspx.