Are you hearing an echo while talking with Skype? Here is a list of ideas based on our own experiences as well as suggestions collected from various forums that may help you. Not all of these ideas may work for all situations, but they would give you a good place to start.
As yet, Skype doesn’t offer an official portable USB version of their software (with the exception of the U3 smart drive version) which frustrates a lot of people (including myself). This has led people to make an unofficial hack of a portable version for themselves.