I am 99% sure I know the answer to this, but I just want to double check.
My domain and forest level is Windows 2008 R2 with this is mind, I should have no problem setting up a trust with another remote domain that is running any forest level version Windows 2003 or greater correct?
Also when a trust is setup this is just the connector between domain and does not grant access to the remote domain resources even if the domain wide authentication level is used correct?
You can create a forest trust between two Windows Server 2003 forests, between two Windows Server 2008 forests, between two Windows Server 2008 R2 forests, between a Windows Server 2003 forest and a Windows Server 2008 forest, between a Windows Server 2003 forest and a Windows Server 2008 R2 forest, or between a Windows Server 2008 forest and a Windows Server 2008 R2 forest.
Configuring Selective Authentication Settings
Trusts that are created between Windows Server 2008 forests can use legacy authentication settings (settings that were used in Windows 2000 Server) or selective authentication. Selective authentication is a security setting that can be enabled on external trusts and forest trusts between Windows Server 2003 forests and Windows Server 2008 forests, in any combination. Selective authentication provides Active Directory administrators who manage a trusting forest more control over which groups of users in a trusted forest can access shared resources in the trusting forest. Because creating an external trust or forest trust provides a pathway for all authentication requests between the forests, this increased control is especially important when administrators need to grant access to shared resources in their organization’s forest to a limited set of users in another organization’s forest.
-- Kindly take a look at the below document, hope it helps.