You can download your Adobe Illustrator Trial here (CS5 version at the time of writing, january 2011)
"The variable line thickener is worth the price you pay for the upgrade."
"The new features are incredible. "
"The isometric (3D) drawing assist tools by themselves make it worth the money"
I can't but agree more. Of all the CS5 new features , Illustrator (along Photoshop one-click background correction tool) is worth buying.