Cannot see Green Button with white arrow in object explorer; DTC config problems?
Your best bet is to download DTCPing (http://www.microsoft.com/en-us/download/details.aspx?id=2868) and run it from both machines.  If I recall correctly, the servers initially talk over the RPC port (135) and then negotiate a random, high port (above 1024) to continue the transaction on.  There is a registry entry that will allow you to limit the ports RPC chooses, but it will apply to all RPC calls not just DTC calls.  http://support.microsoft.com/kb/908472