trouble with aperature setting

[nursequeenie]

I shoot with a nikon d60 with either the kit lens or 55-200.  I find when I try to use the aperature setting, my picture often become overexposed.  The camera is supposed to set the shutter speed for you but I find it often does not work well.  I can manage to get ok pictures with shallow depth of field using the manual setting but not the aperature.  Does anyone else have this issue?
Elizabeth