VFR Tower Controller described a potential separation issue when the Approach Controller failed to insure required separation between two IFR arrivals.

Narrative

I was working the Local Control position; we were active Runway 3. I had a BE33 (IFR) on an ILS approach to Runway 26R on a 3 mile final with instructions to circle to land Runway 3. SCT Approach switched a MU2 (IFR) to me 4 east of the airport on an IFR Visual Approach. I advised the MU2 to make right traffic to Runway 3. The MU2 turned to the down wind 2 northeast of the field and reported that he did not have the BE33 in sight. The BE33 was turning a 1 and 1/2 mile final to Runway 3. I gave him the traffic. The MU2 abeam the numbers for Runway 3 again said he did not have the BE33 in sight. The BE33 at that point was abeam him less by than 1 mile opposite direction. There were no altitude restrictions on either aircraft. Chino Tower is a VFR Tower. We are not authorized to provide separation between IFR arrivals; per LOA. These two aircraft were well within standard IFR separation requirements. SCT needs to train its controllers on proper IFR separation requirements and inform them that we are not authorized to provide IFR separations on arrivals.