Where are the oxygen sensors located on both a 1998 ford windstar and a 1991 honda prelude, any pics are nice?

Why are you asking this? Have they been properly diagnosed? By properly I mean did someone actually test teh vehicels and determine that the oxygen sensors are not functioning? If all that was done is to read teh codes in the computer, then you cannot know if the sensors are bad. Oxygen sensors are voltage generating devices and are often blamed for 'check engine' lights being on. It is realy importnat to know that oxygen sensors never commit suicide, they are always murdered. By that I mean that if they really are not working correctly, then you need ot find the root cause of their problem and fix that before replacing or you'll be seeing more murdered oxygen sensors soon. Think about what can affect an oxygen sensor and you will often find the problem. Use a scantool and get a reading for each O2 sensor: if lean, it could be too much air which could be froma cracked exhaust manifold or leaky gasket upstream from the sensor or the engine may not be getting enough fuel. If rich there may be an airflow problem or there could be oil getting into the system through the intake or past the rings. If inoperative, it could very well be that the sensor is faulty. However, an accurate diagnosis is needed before spending money on sensors that may or may not fix the problem.