Inkscape is a rather nifty tool for creating scalable vector graphics and really good tool to design graphics for linux and fellow unices. A lot of recent icon packages like tango, human (for ubuntu) are made using inkscape.
The first place to check out is www.inkscape.org It has some basic tutorials at http://www.inkscapetutorials.com/ to get you started. If you are more into making icons and related graphics, go check out http://tango.freedesktop.org/Tango_Desktop_Project to get started on the tango icon project on which a lot of modern linux icons are based on. http://www.freedesktop.org/wiki/ provides a more comprehensive look at making icons too. Using http://tango.freedesktop.org/Tango_Icon_Theme_Guidelines is generally recommended if you are interested in making icons.
Here's a video from the page http://video.google.com/googleplayer.swf?docId=-4643787796978610202&hl=en
There is a great web community of web designers specially interested in making scalable vector graphics for it's obvious merits Further resources todo. http://inkscapetutorials.wordpress.com/ has some good tutorials to help you gain some footing.