I recommend you Ubuntu . You can get it over at: http://www.ubuntu.com/
But if you are going to install apache, mysql, mail server its better to go with Fedora Core.
Kbuntu comes with the KDE DE which in my opinion would be a much more suitable candidate for someone coming from windows xp only because it DE is similar to XP. Although i have never used KDE only XFCE or GNOME