There are some cases, like for test and/or labs (but not only), where could be useful convert a local storage to a shared storage compatible with VMware vSphere (or other hypervisors).
For local storage inside the host, the simplest solution is look for a virtual appliance that is designed for this scope (search for VSA – Virtual Storage Appliance). For a storage hosted on a Linux/Unix machine, probably the simplest solution is share the space with the NFS Server (of course it will be limited only to VMware vSphere). And when the storage is on a Windows machine?
For Windows Server 2008 R2 there is the official Microsoft iSCSI Target, downloadable for free (the licence has changed one year ago). There is also a guide to configure the Microsoft iSCSI Target. But this is compatible only with the Server OS and not with the client OS.
In this case, other 3rd part solutions are needed. For example the Starwind product is really simple and fast to configure and works with most Windows version (see the system requirements page). There is the free version, or the trial period of 30 days.
There is also an interesting post: Comparing iSCSI Targets – Microsoft, StarWind, iSCSI Cake and Kernsafe.