By now you have your Mercurial Source Control server up and running, If you go to http://yourserver/admin and log in you should be able to create a new repository. Go ahead and create a test repository and then load up Domino Designer.
Before you can use Source Control in Domino Designer you will need to make sure that you have installed the Source Control Enablement Plugin for Domino Designer V8.5.2. ( if you are on the 8.5.3 Managed Beta this plugin is already installed for you however as it is a beta this capability may not be present in the final 8.5.3 release. The Source Control abilities in 8.5.3 were announced at Lotusphere 2011 with the same disclaimer.). Download the plugin and install it as per the instructions on the OpenNTF website.
The Source Control Enablement Plugin is only half of the solution, all it does is convert the .NSF file into an on-disk project that can be seen by your Eclipse source control system. Once you have installed this plugin you still need to install your Source Control plugin. As we are running a Mercurial Source Control server we’ll need a Mercurial Source Control plugin. Here I recommend MercurialEclipse which is easy to install. Just click on the File – Application – Install menu option in Domino Designer and select the option to search for new features to install. Then in the next dialog box create a new Update Site that points to http://cbes.javaforge.com/update and then click next. Select the new features and install them and restart Domino Designer when prompted. You now have Domino Designer setup for Source Control, in the next section I’ll show you how to link an NSF to your Mercurial server.
As a side note, you can install multiple Source Control solutions in your Domino Designer client, so if you need Mercurial Source Control for one project but need SVN Source Control for another project then this is no problem, you just need to install both Eclipse plugins.