Integrating with project server is as simple as adding a number of web references and calling the right web methods. For more information on the web services available, consult the SDK.

The code below shows how to create a new draft project in project server after authenticating. The first thing I did was to add web references to the project and windows login web services - http://<server-name>/<project-server-name>/_vti_bin/psi/Project.asmx and http://<server-name>/<project-server-name>/_vti_bin/psi/LoginWindows.asmx respectively (the default project server name is pwa). 

        private string baseUrl = "http://portal.sharpcoder.co.uk/pwa/";

        private const string LOGINWINDOWS = "_vti_bin/PSI/LoginWindows.asmx";
        private const string PROJECTWEBSERVICE = "_vti_bin/PSI/Project.asmx";

        private void CreateProject(string username,
                                   string password,
                                   string domain,
                                   string projectName)
        {
            CredentialCache cache = new CredentialCache();
            cache.Add(new Uri(baseUrl), "NTLM", new NetworkCredential(username, password, domain));

            // WebSvcLoginWindows and WebSvcProject are the names given to the web references
            WebSvcLoginWindows.LoginWindows login = new WebSvcLoginWindows.LoginWindows();
            WebSvcProject.Project project = new WebSvcProject.Project();
 
            // Set up login web service and login using windows authentication
            login.Url = baseUrl + LOGINWINDOWS; 
            login.Credentials = cache;
            
            login.Login();
 
            // Set up the project web service
            project.Url = baseUrl + PROJECTWEBSERVICE;
            project.Credentials = cache;
 
            // Create a project data set for the new project
            WebSvcProject.ProjectDataSet dsProject = new WebSvcProject.ProjectDataSet();
            WebSvcProject.ProjectDataSet.ProjectRow projectRow = dsProject.Project.NewProjectRow();
 
            // Probably want to record the guid of the new project in a database or something
            Guid projectGuid = Guid.NewGuid();
 
            projectRow.PROJ_UID = projectGuid;
            projectRow.PROJ_NAME = job.Title;
 
            dsProject.Project.AddProjectRow(projectRow);
 
            project.QueueCreateProject(Guid.NewGuid(), dsProject, false);
        }