I went ahead and installed the Safari 3 beta for Windows, with mixed results: it works fine on XP running under Parallels on my MacBook. It appeared to install and launch fine on my Dell running Vista, but none of the menus appear, and some page content doesn’t show up either. So I uninstalled it from the Vista box. I’ll give it a try later with Vista on the MacBook under Boot Camp.
Update: Here I am updating this post with Safari on Vista, running via Boot Camp. Looks like there’s something wonky with the Dell box. Swell. More time to be spent fixing Windows glitches.