Computing
Computers should be machines capable of performing any calculation you imagine.
Using Unix
If you are using unix for the first time I wrote a small introduction to using unix command line. Also introductions to Linux and free-open source software. Sometimes I add useful sites to a list of computing links. Other people have provided an explaination of Mac OS X.
I also wrote short tutorial for using gnuplot which is a flexible plotting software for producing all sorts of graphs from data or functions.
You can find some desktop wallpapers. I made the 3 linux penguins on a grey background from an image on thinkgeek.com, Thomas made the Mac desktop background.
You can get the first release of pt-group gdm login screen for linux here: PT-group-login-theme.tar.gz be warned it only works properly with rh9, causes problems on rh8, doesnt look as pretty on fedora.