After adding your network card to the modprobe.conf or the MODULES array, you should install the rp-pppoe package and run the pppoe-setup script to configure your connection. After you have entered all required data, you can connect and disconnect your line with:
# /etc/rc.d/adsl start
# /etc/rc.d/adsl stop
respectively. The setup usually is rather easy and straightforward, but feel free to read the manpages for hints. If you want to automatically dial in on bootup, add adsl to your DAEMONS array.
To install kde/xorg:
# pacman -S kde