The Distributed Transaction Coordinator is a service on the Windows NT
based O/S(s) that must be activated for distributive transactions over a
network between machines.
On server and workstation business class versions of the Windows NT
based O/S(s), such as Win XP, 2k3, Vista, 2k8, etc the service is
present. In order for an application running on one machine to use
distributed transactions over the network with another machine, the
client and the server machines must both be using DTC with the proper
authentication credentials used between the two machines.
In other words and for sure, if there is a Web server farm as an example
the has ASP.NET Web applications running on them that need transactions
with a SQL server machine on the network, the all machines involved must
have the DTC service enabled.
I don't know about MSMQ, but I suspect DTC needs to activated too on the
machines if the application using MSMQ can go ito some kind of queue
transaction state between client and server machines.