You need to run Safari via Rosetta, 'cause Shockwave is a browser plug-in and hasn't been updated to be Universal.
Quit Safari, click on its icon in the Applications folder, and from the "File" men, choose "Get Info." Then check the "Open using Rosetta" checkbox, relaunch the browser, and Shockwave should work.
I would recommend only running Safari via Rosetta when you need Shockwave, though, 'cause it'll run slower in that mode. Uncheck that box for normal, day-to-day browsing.