This plugin requires some functions not yet provided by that latest release of serendipity(time of writing: dec 6 2005) so you could get a nigtly release or just ignore that database entries will not be deleted properly.
next take the OpsBlog.zip and extract it in the plugins folder of Serendipity.
Alternatively you could checkout the latest sources from our cvs reposetory.
Now log in as an administrator and click on "Configure Plugins". followed by "Click here to install a new event plugin"
You will see a list of installable plugins, OpsBlog will be listed under "Backend: Editor". Click on the install button next to it to install the plugin.
The next screen will ask you to fill in some details about your OPS setup. Fill them in as follows:
For username and password fill in a user that has access to OpsProject.
The namespace can be safely ignored unless you've changed something in the OpsProject server configuration explicitly
The las t option; "Only show projects which the user is a member of?" gives you the option of either lsting all projects or just the projects a user is a member of(recommended performance wise).