Due to the framework differences introduced in Win RT, OpenAccess ORM cannot run on the client side in such scenarios. However, we do provide a rich set of Web Services generation functionality that you can use to easily expose your entities to any kind of client application, including Win RT.
Do not hesitate to get back to us if you have any other questions or you need further clarifications.
All the best,
the Telerik team
Q3'12 SP1 of OpenAccess ORM packs Multi-Table Entities mapping support. Check it out.