Why does computer headphone jack not play sound from applications? Control panel plays test sounds from it?

I run Vista and sound still comes out of the speakers and not the headphones when I plug my headphones into the headphone jack. I can test the headphones from the Control Panel Sounds setting and sounds come out perfect from there and tells me when headphones are connected and says they are connected correctly. It is the correct jack and headphones work otherwise. Is there some setting someplace that needs to tell the speakers to turn off when headphone put in that might be off that I need to change? Are there types of headphones that computer will say it is connected correctly but will not trigger speaker switchover? These are headphones form an IPOD.Why does computer headphone jack not play sound from applications? Control panel plays test sounds from it?
I do not have any experience with Vista, but I know XP has a panel for adjusting the sound levels for different devices. Make sure all the ';Mute'; boxes are clear.Why does computer headphone jack not play sound from applications? Control panel plays test sounds from it?
that's ur problem.... windows hates appel... so i will not connect with ur ipod head sets =[