sniffing skype is not trivial, because (most) traffic is encrypted... but there are some ways to capture skype traffic. If you like it difficult, take a look at the Black Hat Europe 2006 page
blackhat.com/html/bh-media-archives/bh-archives-2006.html#eu-06
Speak:
Philippe Biondi, & Fabrice Desclaux
Silver Needle in the Skype



