Source: http://feeds.gawker.com/~r/lifehacker/full/~3/237586849/integrate-skype-im-into-pidgin
Windows/Mac/Linux (All platforms): Multi-protocol instant messaging client Pidgin can do a lot of things, especially through built-in plug-ins, but has yet to integrate internet calling service Skype into its offerings. Enter the Skype API Plugin, an early attempt at getting Skype's instant messaging features working in Pidgin (or Adium for OS X users). The good news: It's relatively easy to install and actually works. The bad news: Voice calls can't be made from Pidgin, and you have to keep the Skype application running in the background (which you might do anyways to make and receive calls). The plug-in also imports every out-call and phone contact in your Skype account as a contact, so heavy Skype users might keep this plug-in disabled by default. All in all, however, it helps reduce the number of contact windows on a desktop and provides a promising early look at (hopefully) tighter integration. The Skype API plug-in is a free download for Windows, Mac and Linux systems.