Hi!
Many people out there have problems with skype, because skype uses (deprecated) oss instead of alsa. The next problem is, that skype doesn't work with aoss so we don't have softwaremixing. Skype Developers know about these problems and will release a version with alsa support (hopefully). Just have a look into the skype forums
here. There are also many workarounds/howtos adressing skype sound problems.