MS DTC - Enabling Network Access
If like most people you're development environment consists of both SQL Server and IIS on the same machine you're likely not going to run into any issues with the transaction controller. However, once you split out the database and the application to separate servers you'll start getting some nifty error messages like "network access for Distributed Transaction Manage (MSDTC) has been disabled" etc.
Turns out that if you are using transactions from within your .NET code not only do you need to ensure that the MSDTC service is actually running you need to make sure that it is running on both the client (i.e. application server) and also the database server!
Depending on what server OS you are running checking getting to the settings page changes slightly, but it's basically via Component Services, and you right click on My Computer and select the MS DTC tab. Microsoft support has details on doing so for Windows Server 2003.