If the headphones are giving you sound, they are being detected. Just some headsets don't show up as a listed device.
Try going into "Control Panel" and click "Sound". On the "Playback" tab right click in the white area of the middle of that window and make sure both "" and "" are checked. Should this not make them show, then there may not be a way, however if you right click on the "Speaker" option in that same window and click "Disable", the headphones should still work when in. And the speakers should work when you take the headphones out.
To see if anything shows for volume, right click on the speaker in the task bar and then click "Open Volume Mixer". There should be a volume control for them there, otherwise you would use the...