Create a SharePoint workflow history entry

public void CreateWorkflowHistoryEntry(string Outcome, string Description, string OtherData)

{ SPWorkflow.CreateHistoryEvent(workflowProperties.Web, workflowProperties.WorkflowId, (int)SPWorkflowHistoryEventType.WorkflowComment, this.workflowProperties.OriginatorUser, new TimeSpan(1), Outcome, Description, OtherData);

}

http://www.sharepointbuzz.com/archive/2009/01/21/how-to-create-a-sharepoint-workflow-history-event.aspx