i had the same problem people. the catch for me was that i had wiped the vista that came with my acer and installed xp home. so i had to go to the website and figure out which drivers i needed. there are two places you can download drivers from:
http://support.acer-euro.com/drivers...k/as_3680.html
and
http://www.acerpanam.com/synapse/forms/Acer_drivers.cfm
on the first site, i download the audio driver that was available, and thought i was done. then came the headphone problem. through much search in forums, and stuff...i found the other site, and apparently there is another driver. checked that site, and downloaded the other driver (the realtek hi def one, and the audio driver, and now my problem is fixed.
NOTE: it hasn't been that long since this happened, so i hope it is permanent, but so far so good..
hope this helps.