Couple of free alternatives to Adobe Illustrator:
Inkscape
http://www.inkscape.org (I have this one installed, but don't have talent enough to do anything but make doodles).
Karbon14
http://www.koffice.org/karbon/ (This was originally called Killustrator but Adobe, understandably, objected to the name. The KDE team starts all their projects with a 'K', btw).