Once you get used to the Eee you will soon want to use additional software that is not in the official repositories. To add a new repository simply edit your /etc/apt/sources.lst and add a repository, e.g.
deb http://ftp.de.debian.org/debian/ stable main contrib non-free
Caution: Additional repositories may screw up your system so do this at your own risk. I recommend to disable the repository when not needed once you have installed the desired software.
Xandros recommends not to install any KDE related software from third party repositories because this may lead to an inconsistency in your libraries. Before installing software, always check if the package manager will try to update an previously installed software. For stability reasons, i hardly recommend not doing this.
After adding repositories a simple apt-get update will fetch the new packet list and you can browse the mirror using apt-cache search *packetname*
Some Packages i added safely:
Network: xchat, nmap, aircrack, aircrack-ng, airsnort, kismet, tcpdump, iperf, etherape
Misc Tools: htop