Very simple mod. Skype messages will appear in Minecraft chat with a blue [Skype] prefix. This is a clientside mod, so it works on servers as well as singleplayer.
Installation is a bit different; you will need the Skype API in your mods folder as well as this mod. The download be a zip file. Put both files into your mods folder.
After that, you will need to start Minecraft. On Skype, it will ask you if you want to allow "javaw.exe" to access Skype. After you press okay, you will need to restart Minecraft. Now, it should be working fine.
