For about three out of four I know the answer.
1. Skype protocol was supported in the past, but that was only audio, If you still want skype you can download the skype client for linux from their website.
2. MSN as well as Yahoo video are supported according to the following page on the kopete wiki:http://wiki.kde.org/tiki-index.php?page=Kopete%20Webcam%20Support
But you will have to make sure that your webcam is also functioning on linux.
3. For MSN you could also try using aMSN it also has webcam support.
ps. If it doesn't work feel free to post again in this topic.