Windows 7 laptop's volume with headphones way too loud
It depends on the soundcard, but laptop adapters usually come with an output limiting function to protect the little speaker(s) they have. It should also limit the output to the earphone jack as well:
Maybe something like http://www.amazon.com/Koss-155954-VC20-Volume-Control/dp/B00001P4XH or something similar is what your looking for