how do I access iTunes Visualizer options?
Have you upgraded to Lion?
As per this support thread it seems the extra visualizers require 32-bit mode:
Right click on iTunes.app in your Applications folder and click "Get Info". In the window that appears, click "Open in 32-bit mode" at the bottom of the "General" pane.
This is a work-around, not a fix, and I have filed a bug report with Apple.