If you have a small office and need your office manager to fill multiple roles, it's critically important to make sure that this individual is fully aware of the numerous potential liabilities inherent in human resources management. If they aren't, an introductory course in HR management is necessary and will provide them with information on recruitment and selection, the basics of employment law and compensation, benefit plans, the employee orientation and training process, and performance management and reviews. Until an office manager becomes familiar with these areas, he or she cannot be expected to know when to call in a specialist for additional help.
For more on HR roles, be sure to read Knowing When It Is Time to Get HR Help.