If you are having trouble with the quality of your calls on Skype, here's a tip that may help. Delete the settings.xml file used by Skype. You can find this file by searching for settings.xml and looking for the result (there will be many) that lives in a Skype directory. Or you can open Windows Explore and go to Documents and Settings > YOUR USER NAME > Applications > Skype and you'll find the file in there.

This file contains information about the Skype nodes that will be used for your calls. If you are not using the optimal nodes for your location, this can lead to poor call sound quality. When you delete this file, it'll be automatically regenerated next time you start Skype. If you weren't previously using the optimal nodes for your location, hopefully it'll find the correct nodes when the file is built and this will improve your sound quality. If it does not help the call quality for your Skype calls, then nothing is lost as a result.